Franco was 21 years old when he played High School student Danny Desario on Freaks and Geeks.
O'Brien was 20 years old when Teen Wolf Premiered in 2011
Chad Michael Murray was 22 years old when One Tree Hill Premiered
She was 20 years old when Buffy the Vampire Slayer premiered in 1997
Cameron Monaghan was 17 years old when he was cast as Ian Gallagher in 2010
Vanessa Hudgens was 18 when High School Musical premiered in 2011
Blake Lively was 19 when Gossip Girl premiered in 2017
Christopher Mintz-Plasse was 17 when Superbad premiered in 2007.
Aubrey Plaza was 28 when the To Do List premiered in 2013
Heath Ledger was 20 years old when 10 Things I Hate About You in 1999
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