The website usedwigs.com has an interesting list of the oldest actors that have portrayed high schoolers in movies or TV shows.

The list includes:

Olivia Newton-John and Stockard Channing in Grease.

Olivia was 30 years old…..Stockard was 34!

Alan Ruck was 30 when he portrayed Ferris’ buddy Cameron Frye in Ferris Bueller’s Day Off.

Gabrielle Carteris was 30 on Beverly Hills 90210.

and, Jon Heder was 27 when he portrayed Napoleon Dynamite.