Matt Damon, 43, played 18 year old Scott Thorson in Behind the Candelabra. (Photo courtesy of HBO)
Sean Patrick Thomas was 30 when he played 19 year old Derek Reynolds in Save The Last Dance. (Photo courtesy of Paramount Pictures)
Rachel McAdams was 25 when she played 17 year old Regina George in Mean Girls. (Photo courtesy of Paramount Pictures)
Trevor Donovan was 31 when he played teenager Teddy Montgomery in 90210. (Photo courtesy of The CW/Jaimie Trueblood)
Stacey Dash was 29 when she played 16 year old Dionne in Clueless. (Photo courtesy of Paramount)
Olivia Newton-John was 29 when she played Sandy in Grease, John Travolta was 23. (Photo courtesy of Paramount Pictures)
Jennifer Grey was 27 when she played 17 year old Baby in Dirty Dancing. (Photo courtesy of Vestron Pictures)
Ian Somerhalder was 38 when he stopped playing 17 year old Damon in Vampire Diaries. (Photo courtesy of Warner Bros)
Nicola Coughlan was 31 when she played teenager Clare in Derry Girls. (Photo courtesy of Channel 4)
Emma Thompson was 35 when she played Elinor Dashwood in Sense and Sensibility. (Photo courtesy of Columbia Pictures)
Leonardo DiCaprio was 28 when he played 16 year old Frank Abagnale in Catch Me If You Can. (Photo courtesy of DreamWorks)
Jon Snow is meant to be 14 in the first Game of Thrones book, Kit Harington was 24 when he started the role. In 2018 he's 31. (Photo courtesy of HBO)
Barbra Streisand was 41 when she played a 17 year old in Yentl. (Photo courtesy of MGM/UA Entertainment )
John Cho was 37 when he starred as 21 year old Sulu In Star Trek Beyond. (Photo courtesy of Paramount Pictures)
Stockard Channing was 34 when she played 17 year old Rizzo in Grease. (Photo courtesy of Paramount Pictures)
Rebel Wilson was 31 when she played college student 'Fat Amy' in Pitch Perfect. (Photo courtesy of Universal Pictures)
Actors that were way too old to be playing teenagers
