Kenneth Lonergan’s keenly observed This Is Our Youth, about growing up on the Upper West Side in the 1980s, closes on Broadway on January 4. The date may also wind up marking the end of another era. During the past decade, Michael Cera has come to represent “our youth” to many who identify with the slightly awkward, wholly ingenuous high schoolers he’s played in Arrested Development, Superbad, Juno, Nick and Norah’s Infinite Playlist, Scott Pilgrim vs. the World, and Youth in Revolt. At 26, he may be a bit long in the tooth to play a teen, but the light-voiced Canadian adopts no affectations to pass as Lonergan’s 19-year-old hero, Warren Straub. Instead, Cera has used the six-month run to burrow ever more adeptly into the maladroit slacker’s humiliations, hurts, and romantic heart. In a fall season dominated by splashier productions, This Is Our Youth, like Straub himself, has been somewhat neglected and undervalued, but it deserves to be seen, especially for Cera’s disarming performance. He pulls off complicated bits of stage business with an aplomb that confirms his prowess at the physical aspects of performance. If his Broadway debut ends up being a farewell to the kind of characters who’ve made his reputation, it’s a remarkable valediction. I spoke with Cera before a matinee about his newfound experience as a stage actor and Brooklynite, his camaraderie with co-stars Kieran Culkin and Tavi Gevinson, as well as his plans post-Youth.