While some actors are closer in age to their character counterparts, others can be two or even 15 years older than the characters they portray.
Here are 11 celebrities who are well-known for their teen roles, even though they weren't teens at the time.
Troian Bellisario plays Spencer Hastings on "Pretty Little Liars," an 18-year-old high school student.
In real life, Bellisario is 29. She was 24 when she was cast as the high-school junior. The characters graduated in the mid-season finale, and when the series returns in January, it's jumping ahead five years.
Also 0f note: Sasha Pieterse, who plays Alison DiLaurentis, is 19, so when the show returns, she'll be playing an older character.
Minka Kelly played high-school cheerleader Lyla Garrity in "Friday Night Lights."
She was 26 when the show premiered and was 28 when her character finally graduated from high school and headed off to Vanderbilt University. Current age: 35.
Rachel McAdams ruled the Plastics as high-school queen-bee Regina George in "Mean Girls."
She was 25 when she was cast. Current age: 36.
Gabrielle Union played a sophomore high-school student and best friend to Bianca Stratford in "10 Things I Hate About You."
She was 26 when the film was released, while Larisa Oleynik (Bianca) was 18.
The following year, she appeared in another high-school role as the head cheerleader of the East Compton Clovers in "Bring It On." Current age: 42.
Cam Gigandet portrayed Micah, a 20-year-old Christian high-school student who contracts chlamydia in "Easy A."
Gigandet was 27 during filming. Because of his real age, there is an age joke incorporated into the film where Olive (Emma Stone) asks what a "22-year-old" is still doing in high school. Current age: 33.
Chad Michael Murray won the hearts of teen girls everywhere as Lucas, a brooding basketball player with a penchant for writing, in "One Tree Hill."
Though Lucas was supposed be 16 in the first season, Murray was 22 when the show premiered and 26 when his character graduated from high school. In Season 5, the timeline jumped ahead four years. Current age: 34.
Ferris' day off could not be complete without his best friend Cameron, played by Alan Ruck, in "Ferris Bueller's Day Off."
Ruck was 29 when he played Cameron. In comparison, Matthew Broderick (Ferris) was 23 and Mia Sara (Sloane) was 18. Current age: 59.
Benjamin McKenzie's Ryan Atwood was the bad boy with a big heart, whose arrival rocked Newport Beach in "The O.C."
McKenzie was 25 when he landed the role and 28 when Ryan finished high school. Current age: 37.
Stockard Channing earned a People's Choice Award for her role as high-school student Rizzo in the musical "Grease."
She was 33 when she was cast in the role. Much of the cast was older than their high-school counterparts. For example, Olivia Newton-John was turning 30 when she was cast. Current age: 71.
Jason Earles is best known as Miley's goofy older brother on Disney's "Hannah Montana."
But though he was portraying a 16-year-old high-school student, Earles was 29.
Stacey Dash is well-known as Cher's best friend in the cult comedy "Clueless."
Dash was 28 during the filming of the movie, 10 years older than Alicia Silverstone (Cher). Current age: 48.