I'm following Ewan McGregor around an unspeakably trendy coffee shop on Venice Boulevard in Los Angeles. And right away, it's obvious: we're the oldest ones here. You start to clock these things in your middle forties. McGregor turned 46 in March, I wasn't far behind. One minute you're just going about your day, surrounded by the youth and beauty of LA, when you spot some old guy in the corner and think, "Poor bastard, what's he doing here?" Then you realise, "Oh, he's following Ewan McGregor." You've just caught your own reflection. This is middle age. Not that McGregor seems to have noticed.

It was his idea to meet at Deus Ex Machina, not just a coffee shop, but a hybrid habitat for hipsters, the biker kind. Part-apparel store, part-custom garage, it includes a DJ, some surfboards and a bunch of art magazines one of which is titled simply Shit. We're in a Petri dish for pretty people to park their vintage Harleys and Instagram their avocado toast. And McGregor loves it. Not the toast so much as the Harley-Davidsons. Anything to do with bikes for that matter.

He's travelled the world on motorbikes — two epic journeys that became books and TV series, Long Way Round and Long Way Down. (I'm told there's another in the offing which he can't yet talk about.) At home in Brentwood, a few miles down the road from here, he has maybe 12 motorbikes of his own — or is it 14? — he can't remember. And one of his favourite things to do in LA is to jump on his 1971 Moto Guzzi Ambassador, or his 1974 Moto Guzzi Eldorado, and take off through the canyons and down the Pacific Coast Highway. Sometimes he'll even pop in at Deus to ogle the engines and browse the clobber, just as he's doing now in fact, a steaming cup of black coffee in hand.

"Well, this was a fucking terrible idea!" he laughs. We've done a full circuit of the store and there's nowhere to sit. Even at 3pm on a Monday the place is packed because apparently no one in LA has a proper job. So we take our coffees out into the car park, dropping the average age of the place a few notches, and climb into the back of his black Lincoln Navigator to join his driver Frankie, the only person in the vicinity who's older than we are.

"There you go, perfect," he says. "Better! We've got air conditioning, it's quiet. And look, we can see all the bikes from here. Like that black one, Frankie, look. Old fucking Harley. That's beautiful that is. Let's just hear it start up..."

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Navy wool cable-knit sweater, £495, by Burberry. Stone cotton military trousers, £1,020, by Louis Vuitton. Steel Submariner watch, by Rolex, McGregor\'s own

He looks good for 46, McGregor, still boyish and eager. A few creases around the eyes, and a shaved head on account of Fargo season three — which we'll get to in a minute — but it's still the same McGregor from the Nineties, Mark "Rent Boy" Renton from Trainspotting, a face as indelible to the decade as Liam Gallagher, Damon Albarn or Goldie. That movie launched a generation of us into the night shouting "Lager lager lager lager". McGregor was our totem, the pretty-boy junkie with the lust for life, his blue eyes devouring the horizon as though anything were possible. And that's how it felt — we were in our twenties in the Nineties. So, sitting here with him, now, it's hard to suppress a surge of nostalgia, a limitless resource at this age.

"Have you seen that Oasis documentary, Supersonic?" McGregor says. "I wanted to cut my throat. I did! I was fucking bawling at the end. Just take me back, take me back, I want to be in the Nineties again. Because it was a great time to be... well, me! It was! Fucking amazing. If you think about it, the Trainspotting team were the Oasis of the movie world, weren't we? And it felt good. Really, really good, yeah. Which I think was down to Danny [Boyle]. Because we made a change in British cinema, we made people go, 'Fuck, we can do it!' as opposed to all the cool shit just coming out of America. You know?"

For the last couple of months he's been doing press for T2: Trainspotting the sequel, which ought to be compulsory viewing for men of a certain age. Gloriously meta, it has the same actors playing the same characters 20 years on, all of them looking back over their lives the way one does. Boyle says it's about "masculinity over time", or the way men age, which is to say, not well, not with the dignity of women anyway. Us boys refuse to accept that it's even happening, we're so busy trying to relive our prime. And by prime, I mean our twenties, when we didn't care about time because time lasted forever. Now, halfway to 90, we realise that as Boyle says, "Time doesn't care about you, that's the way the equation really works."

But McGregor isn't convinced. "He's right, Danny, men don't let go of this feeling that we're cool and desirable and funny but..." he shrugs. "That's all fine. I don't want to let go of that. I won't! Why should I? No, I mean I know lots of old men who are sexy and cool, I'm going to be one of those guys, I hope. Ha ha!"

So, he's OK with skinny jeans and dyed hair. He'll have a dance if the mood takes him, too. "Yes, yes, I will do that. And I have. I just don't think about aging much. You should behave the way you feel, not the way you think you're supposed to. And I don't feel any different to when I was in my twenties. Not really. It's not that I haven't learned anything, because of course I have. But I still go about life as I did then. I choose my work with my gut and I throw myself into it, as I always have done."

If there's anything to learn from Ewan McGregor — and, of course, there is: he's Ewan McGregor — it's his attitude. The Tao of Ewan. The Ewan approach to life. He's optimistic, open, big-hearted and unafraid. No one took "Choose Life" as seriously as he did. Just look at what he's built since then, how abundant and teeming it is. The big family (a wife and four daughters), the huge career (78 acting credits on IMDb, almost four a year since his 1993 debut), the massive global adventures (two, soon to be three), and an ongoing position as a Unicef UK Ambassador. As his friend, the director Rodrigo García, says, "These are not the choices of a timid person." And yet, McGregor's never overwhelmed, always smiling. "Yeah, I'm a happy guy," he says, grinning. "I'm hopeful, I enjoy people, I've no cause to feel bitter. What for? I'm very fortunate to have had the life I've had."

Give McGregor's mum a bit of credit here. She always nudged him to think big. When he wanted to leave school at 16 to pursue drama, she said, "Yes, go for it." He'd grown up in Crieff, Scotland, a small town near Perth, and neither his mum nor dad were artists (they were teachers). But his uncle Denis Lawson was an actor — the star of Local Hero (1983), a film McGregor has seen 1,000 times. And he wanted to be like him, an actor and bohemian in north London. He got off to a flying start: his first major role was as the lead in Dennis Potter's TV series Lipstick on Your Collar. At the time, he was living in an illegally rented council flat in Homerton, on the Kingsmead Estate, but now with his first payslip he could afford to move to Primrose Hill, near his uncle as he'd always wanted. There was a flat available for £150 a week. "I thought, no fucking way. I mean, I had my first job, but how long would that last? And my mum said, 'Just do it, you'll make sure you can afford it, you'll see.'"

He remembers driving away, looking at the grim estate in his rear view mirror, putting his stuff in his new place and walking up Primrose Hill to take in the view of London. "That was the moment that I thought, 'OK, my life's different now'. I never looked back."

Ewen Bremner, who plays Daniel "Spud" Murphy in Trainspotting, remembers McGregor in those early years. "He was really opinionated," he says. "Everything was black and white: 'That's shit, that's amazing, everyone should do this…' I don't know that he truly believed everything he said. Maybe he felt he had to project strength or something. We were kids, really."

Few actors know Ewan McGregor better than Bremner: they've made five films together — Trainspotting, T2 Trainspotting, Black Hawk Down, Perfect Sense and Jack the Giant Slayer. Bremner was with him through the Nineties, when McGregor lived with Jude Law and partied with Angelina Jolie. His was the house where everyone ended up at the end of the night. As part of a Brit Pack of sorts, McGregor ran Natural Nylon, a production company with Jude Law and Sadie Frost and others. McGregor also met his wife at that time, Eve Mavrakis, and at 24 they were married — their first child Clara was conceived on the Trainspotting set. "Made in Scotland!" But work would pull the Trainspotting gang in various directions and by the time Bremner saw his friend on the set of Black Hawk Down, he was a different man. "He was much quieter and calmer," he says. "Completely changed."

McGregor laughs at this now. "Yeah, because I decided to go sober. I was just trying to figure out how to lead a life without alcohol." (He's not had a drop since.) But another sobering factor was his fallout with Danny Boyle who had passed over McGregor in favour of another boyish looker, Leonardo DiCaprio, for The Beach. McGregor had made three films with Boyle at that point: Shallow Grave, Trainspotting and A Life Less Ordinary. He saw himself as "Danny's actor". And now that it was over, he felt rudderless and hurt. They didn't speak again for nearly a decade.

During that time, however, McGregor became the actor who liked to say "yes"; the anti-Daniel Day-Lewis. His résumé includes virtually every kind of movie, big and small — drama, action-thriller, romcom, art film, tentpole four-quadrant franchise blockbuster. Many you'll remember — the Star Wars prequel trilogy, Moulin Rouge, I Love You Phillip Morris, The Ghost Writer, Beginners. But others made less of a splash — Incendiary, Haywire, Miss Potter, Son of a Gun, though McGregor accepts these as easily as he does the hits. It's no small achievement to have "no regrets" in your middle years.

"I don't believe in wishing things had been different," he says, a little piqued at the suggestion he might. "Your mistakes are your mistakes. It's all part of your path. And anyway, some of my least successful movies in the box office are the ones that have endured in people's minds, like Velvet Goldmine or Stay. Some just weren't very good but that's fine, too. I love working, I don't do it for the box office."

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There's something to marvel at here. Certainly Bremner thinks so. "Whether you're successful or not, this business is destabilising," he says. "It's no picnic. But Ewan's always so calm and solid, you know? I've seen him deal with crises back home or off-set and still be completely professional and good-natured. And you know, I've never seen him in a bad mood about anything."

McGregor's sunny disposition was tested when his directorial debut, American Pastoral, opened to weak numbers and mixed reviews last year. It's harder for directors, obviously, they feel a greater sense of authorship, but even still, McGregor sees the bigger picture. Any adaptation of Philip Roth's dark and difficult novel was going to be a tall order. "It's everything people don't go to the cinema to see," he laughs. "It's period, it's drama, it's based on a Pulitzer Prize-winning book, so it might sound a bit worthy. Yeah, I'm disappointed more people didn't see it, but they released it a week before the election so America just wasn't in the mood. Everyone was watching the news, going, 'What the fuck?'"

It speaks to McGregor's fearlessness that he took on the challenge at all. Attached as an actor, he'd seen several directors come and go over the years; Roth is famously difficult to translate to film. But when it finally landed in his lap, he went to work. He'd twice had a chance to direct in the past and, in his words, "bottled it", so he wasn't going to let this slip a third time. Roth himself has said he liked the film.

Bottling it isn't really the McGregor way. As an actor, he's gone naked as the part demands. We've seen his penis so many times at this point, that it has become an interview trope to discuss "Little Ewan's" developing career. He has also happily played gay more than once, in Velvet Goldmine and I Love You Phillip Morris. When Jonathan Ross squirmed at the thought, McGregor kissed him on the lips. Get out of your comfort zone, that's his motto. It's why he goes on those huge motorbike adventures. When he and Charlie Boorman were served hot bowls of testicle soup in Mongolia in Long Way Around, there are no prizes for guessing who took the first sip. "It's just meat in the end," McGregor said. "But then you've got to watch for the burst."

Fargo is a new adventure for McGregor, his first proper outing on American television. He'd done a guest spot on ER in the Nineties, in which he played a convenience store robber, but that doesn't count. And in 2012, he shot a pilot for HBO — The Corrections, based on the Jonathan Franzen novel — but then HBO dropped it, despite a cast that included Rhys Ifans, Chris Cooper and Maggie Gyllenhaal. The Corrections was a turning point for McGregor. He was ready to take the leap into TV, to commit years to a show, hopefully shooting in LA, so he could come home to his family each night instead of languishing in some faraway rented apartment as he did on movies. "It gets harder to do that as you get older," he says. "It gets lonely."

Then one day, while skiing in Utah with his friend, actress Sasha Alexander, they bumped into one of the heads of the FX network, Nick Grad. Chatting at a lunch spot half-way up a mountain, Grad asked McGregor if he'd ever seen the first two seasons of Fargo, and McGregor dismissed the very thought — a glimmer of the opinionated young man. "I said, 'That's a terrible idea, making a TV show out of a successful movie! I don't even want to watch it because I love the movie so much'. But he said, 'We're casting the third season, and we're looking for an actor to play two brothers.' I said, 'Are they twins?' He said, 'No.' And I thought, 'Interesting...'"

Now, he can't stop raving about it. Fargo is "more fun than I've had on a movie set in years!" He loves the concept, the characters, the idea of Fargo as a state of mind, a universe with its own rules. But most of all, he loves the pace of TV and the sheer workload of playing two parts, all those lines to learn, it appeals to the working class Scot in him, to the "Choose Life" gusto with which he approaches his work.

"He has an inner spirit," says Noah Hawley, the show's creator. "It's this very tangible boyishness and enthusiasm. And I think it plays very well, once you take the looks away." Hawley took great pleasure in turning the handsome leading man into Ray Stussy, one of the brothers McGregor plays, a fat, balding parole officer who's besotted with glamorous ex-con Nikki Swango (Mary Elizabeth Winstead). But if anything, it heightens McGregor's appeal.

"He makes Ray so endearing," Hawley says. "Even though he's downtrodden by life, you feel he hasn't given up. He's met this girl, he's got something to look forward to. You feel his positivity. Ewan has this quality where his eyes are very open to us, we can really gauge how he's feeling. With true stars it's about what's happening on their face when nothing's going on. You can watch them in repose and still read their thoughts."

Fargo isn't the first time McGregor has played two parts in the same project. In Last Days in the Desert (2015) a meditative, probing movie by Rodrigo García, son of the late Gabriel García Márquez, he played Jesus and Satan. And, as it happens, McGregor got that job while on holiday, too. A friend of his, a director of photography, had invited a few families to the Yucatan Peninsula, and there was room for one more. So McGregor went along and met García there for the first time. They hit it off.

"I could tell he was very empathic and interested in other people," García says. "A curious person, completely unassuming, like an anti-narcissist. And he looks very young."

That last part is critical. Jesus is in his thirties, so García hadn't considered McGregor for the part at first. After the holiday, however, he felt differently. Which left him with a dilemma. "I can't imagine anything more gauche than meeting on holiday, becoming friends and then saying, 'Will you be in my movie?'" So his producer asked for him, and McGregor responded — from a sailboat in Australia, mind — with his characteristic enthusiasm. Here was a small, esoteric, low-budget indie, a long shot in box office terms by any standard, but McGregor found it interesting from a creative standpoint, and that's all it took. "It's such a beautiful, poetic opening," he tells me. "Just a man walking in the desert, you don't know who it is. It was mesmeric…"

For a month or so, he joined a small crew roving around the southern California desert shooting scenes and capturing moments. He loved it. "He immersed himself in the creative process of this movie, the improvisation, especially," García says. "I'd arranged a trailer for him, that we had to park 20 minutes away, but he said, 'Look, I'm not going to use it, I'll just stay with the crew, so you may as well return it.' He knew we had a low budget. He was the first of the actors to make that suggestion."

García has holidayed with McGregor again. Like so many people, he is enamoured of McGregor's beaming attitude to life. Noah Hawley says he's "the opposite of a diva, he's mostly concerned for other people." García says, "he has problems like anyone, but he approaches his work with great enthusiasm. It's a very practical, let's-get-to-work attitude. I feel that work isn't a crisis for Ewan, where for some actors, playing Jesus and the Devil, it could easily have been. Honestly, if you're working with Ewan and you don't get along with him, you need to figure out what you're doing wrong."

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I, for one, am sold. As soon as he leaves, I'll be returning to Deus, to rejoin the hipsters, because like Ewan McGregor, my clay hasn't set yet and all things are still possible. Choose life. Choose avocado toast. It's hard not to be a little inspired by the man, especially given stories like this one, from Bremner.

"I shouldn't say this really, but on Black Hawk Down one of the actors on set was being a brat, you know? And Ewan, in front of the entire crew, stood up and pointed out in front of everyone what this person had just said. It was pretty cool. I can't say more than that, but take it from me — he's a prince. I feel comfortable saying that. He's true to his word, he's generous, and he'll stand up for somebody if he doesn't feel something is right. You can see that from his Twitter. He's not afraid to speak up."

A sample tweet from April 12: "Mr [Sean] Spicer. You need to fuck off now." On March 13: "[Donald Trump]'s a con man. Fooling his base. He could give a shit about the workers." He's called Boris Johnson a "spineless cunt". You get the picture. There's plenty more. Russian fake news mills, the spying scandals, Trump playing golf. Also Fargo and T2 Trainspotting, and some distressing pictures from Unicef of starving refugees. His boycott of Piers Morgan went viral, and McGregor laughs about it today. "He got really nasty, didn't he! He showed himself." There's clearly no voice on his shoulder cautioning him to stay in his lane. Now, he says, is no time to stay silent. "I do not like what's happening, this swing to the right, the increase in racism. I'll never understand why Americans thought it was a good idea to elect that fucking idiot as president..."

And for a while he rants. You get the sense he could go for hours. As a Unicef ambassador, the topic of refugees particularly gets his blood up. "People are being encouraged by the fucking President of America to turn their back on refugees, so I think we have a responsibility. We're all involved. There's like 65m people displaced from their homes right now. You can't just say, 'fuck 'em.' Well, I can't."

He has a green card, he pays his taxes, "I'm allowed to talk about Trump if I want," he says. Besides, he's a long time resident of LA now. He moved here in 2008, and he has no plans to leave, not while the kids are in school. He loves it. Brentwood reminds him of Crieff in a way, the way the neighbours just pop over. Canyon life is a bit more rural and remote. LA is wonderful motorbike country, of course. And he likes to run along the beach, too, another hobby. Jonny Lee Miller who runs ultramarathons, showed him how to go for 90 minutes instead of just 40, so now he does 10km or so runs, four or five times a week. He does a spot of boxercise every few days. "I'd go to a proper gym but I'm too intimidated. Not the face!" And his favourite part of the day is the school run; he drives his girls in a Sixties Rolls-Royce Silver Cloud II. "It's the car Johnny Depp drove in Mortdecai. I spent day after day sitting in this thing in Shepperton Studios and I loved it. So I bought one when I got home."

This is life for McGregor now. A man in full. Rich with family, accomplishments, creative fulfilment; a life of shared vacations with friends and colleagues, of running along the beach with the sunshine at his back. The world may be falling apart out there, and our man's not getting any younger, none of us are, but he's not getting much older either. He's pressing forward, always forward.

So where now, Ewan? He stops shooting Fargo very soon, then there's a movie by Drake Doremus, Zoe, a love story. But beyond that, he's open. Maybe he'll direct again if he finds the right project. He'll certainly act, he's always looking, his blue eyes still devouring the horizon. What he really wants is to work with great people. He's already worked with Ridley Scott, Woody Allen, Tim Burton, Roman Polanski and he knows he's been fortunate in that regard. But there are particular names on his wish list. Like the Italian director Paolo Sorrentino who created HBO series The Young Pope. "Trouble is, I don't fucking speak Italian... so maybe a mute role. Sorrentino, if you're listening..."

Top of his list, though, is Danny Boyle, his first director and his favourite. There's history there, and yes, nostalgia. "I felt that he defined me all those years ago. Those films will always be part of who I am. And also he's just the fucking best... no one else gets better work out of me."

After years of being estranged, the Trainspotting gang are all back in touch; there's a five-person email that goes around. So something's going to come of it, he's certain. If nothing else, there's always T3 in a decade or so.

"That's it!" McGregor laughs. "The Skagdale retirement home for ex-heroin users. Sign me up!"

This interview appears in the June issue of Esquire, out 30 May.

Fargo season three is on Channel 4 now