Danny Boyle’s Trainspotting, released in 1996, felt instantly mythic. A grubby, inspired adaptation of Irvine Welsh’s novel that stars a vibrant, nearly vibrating Ewan McGregor, the film felt new and breathless and terrifying, a movie about fuckup junkies that didn’t shy away from euphoric highs or moments of extreme bleakness.

If you have watched movies in the past 20 years, you’re aware of Trainspotting. And if you think about it for even a minute, you realize that the manic energy, the drug-fueled intensity, that Trainspotting depicted — it can’t last. It’s unsustainable. It’ll kill you.

So how do these characters keep living?

This is the question T2 Trainspotting is mostly interested in. There’s reminiscing, sure, in a goofy, inevitable scene where Renton (McGregor) and Simon (Jonny Lee Miller) revisit a certain kind of glory days. But there’s also wry honesty, whether it comes from Veronika (Anjela Nedyalkova), Simon’s not-girlfriend, who observes that Renton and Simon are clearly in love with each other, or from Begbie (Robert Carlyle), still furious about the money Renton lifted off his pals 20 years before.

The past is still super-relevant for these guys, but it’s nowhere they need to go back to; they might reminisce, but there’s no longing. Instead, Boyle and screenwriter John Hodge find a crushing honesty in the way these characters’ past colors their present.

Renton explains his motto “choose life” to Veronika, and it’s just as burning, just as angry, but it’s lost its joy: You just have to keep choosing; there’s no getting away from that. He tells Spud (Ewen Bremner), who’s still using, that he has to channel that addiction into something else, and Spud, unexpectedly, becomes the poster child for taking charge of your own narrative — for telling yourself a different story or an old story in a different way. For change.

Some people have seen T2 as a betrayal of the first movie’s exuberant, irrepressible youth, which is almost understandable. But the honesty of this new film has its own kind of vitality. This isn’t glibness, a soulless Judd Apatow take on rich people aging imperfectly. It’s so rare to see a film about adults struggling with adulthood that feels like a life rather than a collection of clichés. (It’s even rarer to see one about women, but Trainspotting has always been a boys’ club — though Veronika shakes that up a bit.)

Scenes from the first movie and from the characters’ childhoods occasionally veer into sentimentality (a trait of the aging Boyle), but mostly they remind us that these guys, like all of us, are the sum of their parts. What do they add up to? What do you do if you don’t choose a family and a starter home and a career and a big television? How do you grapple with growing up and aging — one you have to figure out, and one that just happens to you, if you’re lucky? And how are all of us ’90s kids aging?

The world keeps changing, and we have to keep living in it, lest we wind up like the Catholic-haters Renton and Simon end up serenading, living in a distant past, cut off from the rest of everything, singing songs about the olden days.

Those songs might still be good, but they’re ageless. We — tragically, comically, unavoidably — are not. (Broadway Metro)