It stars Maisy Stella in her film debut, Percy Hynes White, Maddie Ziegler, Kerrice Brooks, and Aubrey Plaza.

Elliott, a teenage girl living on her parents' cranberry farm in Muskoka Lakes, Ontario, has three weeks left before she leaves for university in Toronto.

She spends her summer days boating with her friends Ro and Ruthie, working on the farm, and engaging in a romance with Chelsea, a girl she has had a crush on since the eighth grade.

On a night out camping to celebrate her eighteenth birthday, Elliott takes mushroom tea with Ro and Ruthie; all three experience psychedelic trips.

During her trip, she does not see Older Elliott but hallucinates that she is Justin Bieber, performing "One Less Lonely Girl" and giving Chad red roses.

In March 2022, it was announced that Megan Park would write and direct her sophomore feature film, a coming-of-age comedy titled My Old Ass, with LuckyChap Entertainment and Indian Paintbrush producing.

[9] The film received a limited theatrical release in the United States, originally scheduled for August 2, 2024,[10] but delayed to September 13, 2024.

The website's consensus reads: "A humorous sci-fi cocktail with a twist of drama, My Old Ass doesn't throw out the wisdom with the reckless abandon of youth and the effects are hallucinogenic.

[14] She wrote Stella "has incredible screen presence and a great sense of comic timing, but she's equally convincing playing the more dramatic moments required of her character.

"[14] Lemire added, "Besides crafting characters who feel like real people, Park also creates a vivid sense of place.

The adventures and the enveloping quiet feel personal and specific, but there's a universality to this crucial point in Elliott's life that gives the film unexpected poignancy.

"[15] She praised how the film "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.

"[15] Richard Lawson of Vanity Fair also praised Stella, saying she "makes Elliott a just-shy-of-annoying good-times gal, rude and rowdy but ultimately kind and decent.

"[16] Lawson noted the choice of setting—"the shores and islands of Lake Muskoka in Ontario, [make] My Old Ass a proudly, distinctly Canadian film.

"[16] He concluded, "What Park creates from the tension between this joyful, exciting present and a seemingly ominous future is rather marvelous, a big and sincere sentiment about the risk and reward of life, a message that is just as worthy for a middle-ager as it is for a kid.

Yet she expertly acknowledges the inspiration of our celluloid past, proudly walking in the footsteps of Billy Wilder, Elaine May and John Hughes.