I’m a little worried about Pete Davidson.

Then again, that’s the enduring brand of Davidson, the proudly unstable “Saturday Night Live” comic who’s having a moment with a Netflix special, an upcoming semi-autobiographical Judd Apatow movie and this dramedy. In “Big Time Adolescence,” he’s playing, not against type, a witty, underachieving slacker with a predilection for weed. His character, Zeke, is the short-lived high school boyfriend of Kate (Emily Arlook), whose little brother Mo (Griffin Gluck) gets so attached to him that the boys stay friends long after the couple breaks up. But Zeke also stays, resolutely, a boy, as he ages into his 20s — and he also, frustratingly for Mo’s parents (Jon Cryer and Julia Murney), remains Mo’s best friend.

Director/writer Jason Orley (whose debut was the Davidson special “Alive From New York”) deploys a gradual shift in tone, as Zeke’s disdain for anything resembling adult life goes from amusing to worrisome to just plain sad. What begins as a comedy, with Zeke the kind of zany, inappropriate older-brother figure every socially awkward kid might dream of, drifts into darker territory. (I imagine your age will be inversely proportionate to how quickly you start to find all of this upsetting.) When Zeke comes up with the bright idea of having Mo sell pot at high school parties, you know things are headed south.

Gluck (“Locke & Key”) is smart and precocious and a little square, cut from the Joseph Gordon-Levitt mold. Mo’s insecurities make him the perfect follower of Zeke, who may lack for a decent job or the ability to remain faithful to a girlfriend, but never for confidence. The musician Machine Gun Kelly shows up as one of Zeke’s lowlife friends, who seem to be endlessly eating greasy takeout, drinking crappy beer and playing video games. What’s for a teen boy not to aspire to?

Davidson expertly plays the role like he’s playing . . . well, Pete Davidson, which is how I imagine his career will go. (It’s certainly worked for other comics. Has Kevin Hart ever played anything else?) Having gone public with mental illness and addiction struggles, he brings a believable note of pathos to Zeke, whose reaction to a modernist painting hints at some sophisticated darkness: Life is “just a bunch of scribbles and d - - ks and violence, all in a void,” he says. Ultimately, though, he can’t escape his own juvenile impulses — hence the title, perhaps. In any case, I’m still going to worry about Davidson.