At 20 years old, Maisy Stella has already lived several lives. As a TV actor, she co-starred on Nashville from the age of 8 to 15, while, as a child musician, she was a viral sensation who inspired Billie Eilish to start performing. With My Old Ass, her movie debut, Stella is now entering the world of cinema having already been famous for most of her existence. After all, in 2015, she was interviewed by the Guardian as an 11-year-old about a book she co-authored. “Oh my God,” she says in horror when I bring up that she referenced adoring The Fault in Our Stars. “I don’t remember what I said in that at all.”

I’m speaking to Stella in London in early June, just a day ahead of My Old Ass screening at Sundance London. Bought by Amazon for $15 million in January, Megan Park’s queer coming-of-age film features Stella in practically every scene, even if she’s only half of the main character. Full of boisterous energy, the actor plays Elliott, a loquacious 18-year-old who takes mushrooms and is greeted by the 39-year-old version of herself. Depicted by Aubrey Plaza, the senior Elliott has travelled back in time to shower advice upon Stella’s character: spend time with relatives, appreciate the moment, and, crucially, avoid anyone named Chad.

The beauty of Park’s sci-fi concept is that the time travel is never questioned, just accepted with a shrug. The young and old Elliott don’t plan get-rich lottery schemes, nor do they fret about any butterfly effect. When they stay in touch by phone – Plaza’s Elliott inserts her number under the name “My Old Ass” – the logistics are easily swept aside. Even if Stella and Plaza barely look alike, they could conceivably be the same person through their shared sardonic humour.

“I’ve so much respect for the risk they took in making Aubrey be my future self,” says Stella. “She embodied so perfectly a toughened, hardened version of Elliott who’s been through some shit.” Whereas Stella’s background is in drama and music, Plaza comes from comedy and sitcoms. The connection was identified, Stella believes, from their real-life personalities. “I was the first person attached to this movie, and I’d been filming for two weeks before Aubrey was added. We had talked to so many people but Megan kept coming back to Aubrey. They believed in it, and I believed in it: when we were filming, we really did have such an aligned energy that felt special.”

The older Elliott’s warning about staying away from anyone called Chad comes to fruition when the younger Elliott has a meet-cute with a guy whose name is, yes, Chad. Played by Percy Hynes White, Chad is harmless, anxious, and, to Elliott, possibly the first guy she’s ever been attracted to. In a comic subversion of movie tropes, Elliott worries to her BFFs that there might be a tiny part of her that’s straight; her pals assure her that it’s OK either way.

“I was so drawn to Elliott because there was this openness, this liveliness, this eagerness to explore, experiment, and dive deeper into who she is,” says Stella. “Megan wanted it to feel genuine, and she cast primarily queer people in the film. She did a splendid job. We’re in a generation where there can be pressure around labels. Relieving yourself from that, and allowing yourself to be open, is literally the entire basis of the movie.”

I didn’t realise until watching it back that you can watch it from either side. I hope the old asses of the world can take something from the young ass – Maisy Stella

While Stella comes from a musical family – her parents perform as The Stellas, and she duets with her sister Lennon as Lennon & Maisy – she describes her upbringing in Oshawa as “not really of any wealth”. Aged seven, Stella performed a cover of “Secret” by Miss Higgins in which she played guitar and sang like someone way older than seven. On Instagram, Billie Eilish cited a YouTube video of Stella’s rendition of “Secret” as the catalyst for her career: at the age of 11, Eilish entered a talent show doing “Secret” in an almost identical fashion to Stella.

As for who Stella looked up to herself, she tells me that her early obsession was the movie Labyrinth, one of a handful of VHS tapes she owned, and that otherwise it was playing make-believe at home. “My sister Lennon built a cardboard box TV and a had a fake remote. I would get inside of it and, for hours, be acting out different scenes.” When Nashville ended, though, Stella was 15 and ready to pause her career. “Taking a break and going back to school was the most important thing I ever did. It made me feel very human.”

After three years away from showbiz, Stella won the role on My Old Ass with an elaborate self-taped audition that included a tour of a tiny boat she owns, all to prove how similar she was to Elliott. “I sent in way more than they asked,” Stella admits. “I was pulling any trick to get their attention.” No gimmicks were required, though, for Stella’s second film, Flowervale Street, which she wrapped two days before our interview. “The producers had seen My Old Ass, which really helped.”

Written and directed by David Robert Mitchell, Flowervale Street is a sci-fi blockbuster designed for IMAX screens in 2025. “It’s a very intense movie,” says Stella, who co-stars with Anne Hathaway and Ewan McGregor. “I’m still processing the ending of it.” Will Mitchell, the auteur behind It Follows and Under the Silver Lake, have to tame his idiosyncracies for the multiplex? “I don’t think he could make something that doesn’t look like a David Robert Mitchell film. There hasn’t been a movie about what this is about, done with this artistic style.” Can she confirm the rumour that dinosaurs will be involved? “I don’t know if I can say. No comment!”

In the meantime, My Old Ass will get a wider release to the public, many of whom will have to determine whether they identify more with Stella’s Elliott or Plaza’s Elliott. Alternatively, there are lessons to take from both characters: while the premise revolves around the younger version learning from her elder, it ultimately leads to the 39-year-old Elliott taking inspiration from her teenage self’s go-getter attitude. “I didn’t realise until watching it back that you can watch it from either side,” says Stella. “I hope the old asses of the world can take something from the young ass.”

My Old Ass is in UK cinemas on September 27