My Old Ass has the premise of a broad comedy and the soul of a bittersweet coming-of-age story. And one of the reasons that it works so disarmingly well is that it doesn't treat the former as a means of sneaking in the latter. Writer-director Megan Park is genuinely interested in the emotional potential of the idea of being able to communicate with your younger self. Is there advice you'd want to give if you could? And would the earlier version of you even want to hear it, if so? The burst of magical realism that puts 18-year-old Elliott Labrant (Maisy Stella) in contact with her 39-year-old future self (Aubrey Plaza) does lead to some funny moments, like when the teenager demands to lock lips with her double. ("You don't want to know what it's like to kiss yourself?!" she asks, half faux and half genuinely outraged.) But My Old Ass takes a grown-up's fantasy of getting the chance to retroactively apply the wisdom of your years to undo the mistakes of the past, and then turns it around to be a celebration of being young and heedless, with no clue what you're doing. It's an affectionate rebuke of the impulse behind helicopter parenting, even if in this case, the person trying to shelter Elliott is Elliott herself.

Elliott's a rambunctious girl who's running out the last weeks of summer on her family's cranberry farm on Lake Muskoka before heading to Toronto for college (My Old Ass is quietly but powerfully Canadian). While she hasn't been shy about announcing her eagerness to leave to anyone who'll listen, her home is downright idyllic -- a community perched on a glassy waterfront, peppered with small businesses and islands where three teenagers can camp out for the night to do magic mushrooms. It's while doing precisely that that Elliott meets her future self in an encounter whose mechanisms neither she nor the movie is inclined to dig into. Midway into her high, Older Elliott just turns up on a log by the campfire, and after verifying her identity by confirming the exact cup size difference between their boobs, begins chatting. She refuses to share stock tips or too many details about what's to come, and the recommendations she does have mostly involve Elliott spending more time with her family. But she does offer one serious warning -- to stay away from anyone named Chad, which becomes relevant when a fine-boned undergrad (Percy Hynes White) called exactly that turns up as a summer worker on the farm.

Plaza doesn't look like someone Stella is going to grow up to be, but her teasing, deadpan affect suits the character, who's trying to talk like a kid, but who also doesn't quite think of herself as an adult yet either. When she tries to urge Elliott to appreciate what she has, she does so by earnestly intoning "The only thing you can't get back is time -- when you get older, it goes by so fast, dude, so fast, it sucks." But despite a running bit about how much worse the Earth that Older Elliott lives in has gotten (where did the salmon go?!), she's really there as a reflection on what her younger self is going through. And present day Elliott, played with lived-in ease by Stella, is a winning creation, in all her brash confidence and bursts of obliviousness -- someone who, in contrast to typical depictions of teens as only half formed, is so certain of who she is that she's aghast when anything threatens to reveal she has more to learn. One of those threats comes from Chad, who despite Elliott's initial leeriness, turns out to be thoughtful and charming in a way that makes her question if she's actually gay, as she always took for granted. Older Elliott's warning hangs dolefully over their budding romance, but that doesn't stop Elliott from charging ahead as, we learn, she's always been prone to do.

Getting hurt is part of growing up, and part of life, and if that doesn't seem like it should be a controversial point, My Old Ass emphasizes how much harder it is to commit to when the person getting hurt is someone close to you -- like, say, your younger self. Park's film is modest, but it's grounded in the inner terrain of its characters in a way that makes it feel substantial. Sometimes this means acknowledging the pain you've inflicted on others, as Elliott does during conversations with her parents about the future of the farm that make her aware of the inadvertent slights she'd been inflicting with all her eager declarations of independence. Elliott, as she says herself, can be a bit of an asshole. But she's 18 and has a lot of growing up to do -- enough to still be growing 21 years from now.