Hollywood is notorious for casting older actors in roles that are meant to portray high school-aged students and teenagers. Sometimes it can get so wild that you find yourself watching people play a character that's half their real age.

So, here are 13 adult actors who took the fountain of youth to a whole new level and portrayed teenagers on-screen, and 12 then-teenage actors who actually got cast as teens:
1. Adult: Audrey Hepburn

2. Teenager: Lindsay Lohan
