The surprising real ages of actors when they were cast in famous teenage roles

Mean Girls' Regina George (centre), played by Rachel McAdams, is the "meanest" high school character of all time, according to Sky Q research.

Age is but a number, and you don't have to be a teenager to play one on TV or film.

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 12 celebrities who are well-known for their teen roles, even though they weren't teens at the time.

Troian Bellisario was cast as Spencer Hastings on "Pretty Little Liars," an 18-year-old high school student.

In real life, Bellisario is 30. She was 24 when she was cast as the high school junior. The character has since graduated college after a five-year time jump.

Troian Bellisario is less impressed with Swift (Getty Images)

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: 36.

Minka Kelly, left (Screen Gems, Inc)

Rachel McAdams ruled the Plastics as queen bee Regina George in "Mean Girls."

She was 25 when she was cast. Current age: 37.

Mean Girls' Regina George (centre), played by Rachel McAdams, is the "meanest" high school character of all time, according to Sky Q research.

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: 43.

Gabrielle Union was targeted shortly after getting married (Getty)

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's a joke incorporated into the film where Olive (Emma Stone) asks what a "22-year-old" is still doing in high school. Current age: 34.

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. Current age: 35.

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: 60.

(Rex Features (Rex Features)

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: 38.

Lea Michele played the spunky and somewhat obnoxious high schooler Rachel Berry in "Glee."

She was 22 when the first episode aired. Current age: 30

(Getty Images)

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. Current age: 72.

Much of the "Grease" cast was older than their high school counterparts. For example, Olivia Newton-John was turning 30 when she was cast.

Jason Earles is best known as Miley Cyrus' goofy older brother on Disney's "Hannah Montana."

Though he was portraying Hannah Montana's teen brother, Earles was 29. Current age: 39

Stacey Dash is known for being 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: 49.

A still from the 1995 film 'Clueless'

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