Ramsey, 22, is best known for their role as Lyanna Mormont in Game of Thrones
Bella Ramsey spent many teenage years working with adults so never really went through the moody, rebellious phase often associated with being a teenager.
The British actor, who debuted in Game of Thrones aged 11 and uses they/them pronouns, says they had consciously decided not to behave like a stereotypical teenager after hearing criticisms from adults.
So when Sunny Dancer, a film about a summer camp for young people affected by cancer, gave Ramsey seven weeks to experience teenage freedom, it was an opportunity to dive straight in.
"I got to be a teenager aged 21, which was brilliant," Ramsey tells BBC News. "It was really nice – and liberating."
Looking back, Ramsey says the experience made them wonder whether they had missed out by being quite so sensible the first time around.
"I kind of wish that I had made the most of being a teenager and getting away with things and being a bit rebellious."
In Sunny Dancer, Ramsey plays Ivy, a young female cancer survivor in remission who reluctantly heads to a "chemo camp" where she finds an unexpected group of friends and has a summer that changes her.
Sunny Dancer also stars Neil Patrick Harris, Jessica Gunning and James Norton
The rest of the cast were more than happy to help fill in the gaps; Ramsey says younger co-stars discussed songs and nights out.
"They were teaching me what being a teenager was for them and I was learning all the songs like five years later."
Beneath the summer camp fun is a story that is deeply personal for the film's writer and director, George Jaques.
His mother was diagnosed with cancer when he was 15, but it took another eight years for him to feel ready to turn some of those experiences into a script.
"I never seem to write in the moment I'm going through it," Jacques says. "You have to sort of get through and understand it and have that reflection of it."
He stresses that the film is not his family's story, but "there's bits of me" scattered throughout its characters.
