Who'd be seventeen again? A cast of 'veteran' actors, in Aussie Matthew Whittet's sweet play about the last day of school. A group of teenagers worry about the future, angst over who fancies who, and show a commitment to getting "shit-faced" on vodka which translates to the UK without any, er, straining of credibility.

Initially, the age gap between these mature actors and their immature characters seems like a one-note joke: the blokes, especially, overdo it with cackling laughter and inflated yoof-ish gestures. Scenes dancing to Rihanna songs can feel like pretty cheap look-at-the-old-people-groove jokes (although props to Diana Hardcastle and her thighs of steel). There is a whiff of Kevin and Perry to it all.

But while Whittet's play is never exactly profound, it certainly reminds you of how everything seemed terribly profound when you were a teenager: how deeply you felt things, how incomprehensibly huge a deal it was finishing school, how fiercely you loved your friends. By putting words into the mouths of people with plenty of life experience, they attain a certain wry distance. This gently highlights the humour of teenage exaggeration and fatalism ("I'm going to die," insists one after drinking too much), but the wistfulness dials right up too. Lines about solemn regrets or fears that the future is already tediously mapped out inevitably take on a new note of yearning when delivered in the croakier voices of actors in their sixties.

The play doesn't feel especially of its moment; phones are barely used beyond the odd selfie, and little attempt is made to capture any contemporary vernacular beyond a shit-load of swearing. But as we get to know the teenagers, Anne-Louise Sarks' production does become steadily more moving.

At first I thought Mike Grady struggled to make sense of school weirdo Ronny, but a late confession of self-loathing is just heart-clenchingly sad. As best mates Jess and Emilia, Hardcastle and Margot Leicester are both very good, the former capturing the switches between sexy poise and excitable girlish gestures of someone just turning 18, while the hangdog, deadpan Leicester makes her swottier character absolutely the funniest onstage. Sarah Ball is also very enjoyable as Lizzy, a 14-year-old little sister who hangs around like a fly; she's a buzzing mix of irritant and sage.

They all twirl and clamber over a giant children's playpark, with a neat infinity-symbol shaped climbing frame and a set of tall swings, designed by Tom Scutt. The kiddie setting prompts their own damp-eyed reminiscing, even at the tender age of 17; it's a reminder that however old you are, there's always something to look back on sentimentally.

Yet nostalgia would be the wrong word for this play - although Seventeen captures that moment of hovering possibility between school and the rest of your life, by casting older actors it doesn't just present a picture of youth, a window to step back through. You're constantly reminded of what a fleeting moment it is, how time trundles on. And thank god: no-one would really want to be seventeen again.

Seventeen is at the Lyric Hammersmith until 8 April.