In the hotly anticipated high school horror flick "Jennifer's Body," Megan Fox plays a cheerleader with a heart of darkness. We have no doubt she'll look extra sexy pumping pom-poms and killing male classmates, but at 23, she's also a bit long in the tooth to play a teenager. Not to mention her co-stars Amanda Seyfried, Adam Brody and Chris Pratt are also all in their mid-20s to early 30s. C'mon Hollywood, we weren't born yesterday.
In honor of the back-to-school season, we've compiled a list of the Top 10 oldest celebs ever cast as high school students and college coeds on-screen. Grab your calculators, boys and girls, and prepare yourself for a celebrity math lesson!