Maisy Stella was 8 when she was cast in “Nashville,” a role that went on for six years.

Now 20 and starring opposite Aubrey Plaza in the feel-good coming-of-age drama “My Old Ass,” Stella plays Elliott, who is celebrating her 18th birthday by tripping on mushrooms with her two best girlfriends on a tiny island near her home.

“It’s a big time in Elliot’s life,” Stella said in a Zoom interview. “She’s coming into her own in that time that everyone experiences a wake-up call before you leave home.

“You have all these little epiphanies.  She’s facing the moment where you look at your mom and you just feel kind of sad because you realize that she’s not just your mom, she’s a person herself.”

During her mushroom hallucinations, Elliott performs a rousing Justin Bieber song. Sure, it’s all in her mind but we’re seeing something real. Was that added because she is indeed a singer?

“Yeah! It was so fun to get to do that. Megan Park” – the writer-director – “wanted there to be some type of a musical comedy bit. It was originally a Disney song, only they couldn’t get the rights to that obviously, because I’m doing drugs in the scene.”

It’s after that experience that Elliott somehow meets herself – at 39! As played by Plaza, this older Elliott offers guidelines on how to embrace her future.

“We didn’t overthink our process together of being the same person. We just led with humor and connection.”

As to how Stella has embraced her past, when did child’s play become a real career?

“I have very, very early memories of me knowing that this is what I wanted to do. We grew up (in Ontario, Canada) without any cable or any TV.

“The first TV that we bought was the day that we were on TV! My sister would make like cardboard boxes that I would get inside of, and we’d pretend that it was a TV and I put on performances.

“Nashville,” she remembered, “ended up going from the time I was eight to 14. It was just really long. When it ended, I went back to school and really just made sure my head was on tight.

“I lived my life as a teenager and didn’t put any pressure on myself to be working. And that’s when I really fell in love with it again and really wanted it for the first time — because I didn’t have it.

“I was so eager to get back into it and this project was the most perfect, in the softest landing, for me to re-enter.”

“My Old Ass” is in theaters