What is Zac Efron? Despite his ubiquity and supernova stardom in certain shrieking demographic circles, I feel confident that there are others who are curious about this weighty question of culture.

For starters Zac Efron is a he, a Californian by birth and of drinking age in the state of his birth (21). He is pale, pliable and very pretty (picture-perfect for bedroom walls), with a curtain of hair that sweeps across his forehead and well-manicured dark brows as if gently stirred by the collective exhalation of a thousand virgins. I’m fairly certain I heard that exhalation — I certainly heard the shrieks — when I watched his new movie, 17 Again.

The dewy Efron is also, of course, the most visible star of the High School Musical juggernaut, which has taken him from the Disney Channel to the familiar rite of passage as host of Saturday Night Live. The maturation of Zac Efron, the bid to have him gently (lucratively) transition out of the grip of his pubescent fan base and into the wider commercial paw without pulling a Lindsay Lohan, partly explains 17 Again.

Even the movie’s premise — an adult transformed into his adolescent self — speaks to this uneasy transitional phase, though it seems a little cruel to the fans who must prepare for the inevitable, that someone decided an exhausted-looking Matthew Perry should play their shining boy at 37.

In pop cinema terms that premise is almost as old as Jodie Foster, who starred in the first Freaky Friday (1976) as a girl who switches bodies with her mother. Foster’s preternatural maturity and husky voice made the part work for much the same reasons that the 2003 remake with Lohan did: you believed there were old(er) souls trapped inside those young bodies. Foster and Lohan’s unforced talent helped. A confident physical performer, Efron isn’t in their league, and it’s too early to tell if he ever will be. Although he can hit all the emotional notes in a scene, there is a level of calculation behind his performance and piercing blue eyes, a protective barrier or just self-consciousness that needs dismantling.

Meanwhile he works it — man, does he work it — strutting across the screen like a teen idol (like Zac Efron!), playing the star with an easy smile, insouciant haircut and even bared muscles: his character, Mike, is shooting hoops without a shirt in the very first shot of the movie. (Cue the shrieks.)

The story, written by Jason Filardi, pivots emotionally on the moment when Mike turned his back on a potential basketball scholarship and all the good things that would have presumably come with it because he decided to dry the eyes of his weeping girlfriend, Scarlet (Allison Miller as the teenager, Leslie Mann as the adult).

Given the story’s obnoxious implications — sex, meaning girls, can ruin your life — it’s no surprise that Scarlet doesn’t get the chance to revisit her past and tell her boyfriend to put on a condom. Instead the adult Mike clicks his heels or rather falls into a badly computer-generated whirlpool trying to chase a stranger with a menacing twinkle (Brian Doyle-Murray), who guides him to his journey. Suddenly, Mike is 17 again and sloshing inside his business suit. He takes refuge with his best friend, Ned (a hilarious Thomas Lennon, nearly sprinting away with the movie), a former late-20th-century high school dweeb turned early-21st-century master of the universe who lives in a Modernist house crammed with pricey boy toys and sleeps in a Star Wars landspeeder.

The director, Burr Steers, whose other credits include Igby Goes Down and stints directing TV shows, keeps people and things moving fast enough so that you don’t have time to worry about the details, like the inanity of the story. Like any savvy director charged with a high-end advertising campaign, he keeps his main product — Efron — front and centre and nicely lighted. Even so, Steers also understands the value of his supporting team, particularly Lennon, whose character enters geek heaven upon sighting Mike’s principal, Ms Masterson (Melora Hardin). Mike’s transformation might be magical, but it’s this pocket-size portrait of a sexy, thinking, adult woman who can seamlessly go from wearing high-heeled boots to pointy elf ears that’s out of this world.