Could they pass for teenagers?
Sean Penn (turned 22 the year the film came out) - Maybe. Just barely. Certainly he projects the immaturity of a California surf teen.
Jennifer Jason Leigh (19) - Definitely and easily. Hell, she could easily pass for 15, probably not 14 though.
Judge Reinhold (25) - Absolutely not. I don't even think they really needed to have this guy still be in school in the movie, he could have been doing fast food full time.
Phoebe Cates (19) - I suppose so, I'm stunned she was actually only 18-19, she looked older (and someone on the set apparently mumbled something like "She's actually pretty talented for a model!")
Robert Romanus (26) - GOD NO. Way, way, WAY too old. Hell, he looked too old for COLLEGE. Had it not been for Buddy Repperton in Christine the following year (or possibly Don Dawson in Dazed and Confused), he would be the oldest looking high schooler I've ever seen!
Brian Backer (26) - Certainly. In fact, it's stunning he was born the same year as Robert Romanus. Then again, he is playing the movie's "wuss."
Scott Thomson (28 or 25 depending on where you look) - No way; in fact, I forgot this guy is even supposed to be a teen in the movie. As with Brad maybe he should have been college age and just working the fast food job.
Amanda Wyss (22) - I guess. Again, she and Brad Hamilton come across like college students.
Forest Whitaker (21) - I suppose so. Not much to say about him. The kid playing his little brother was a laugh riot.
Anthony Edwards and Eric Stoltz (20 and 22) - Sure. Weirdly enough Stoltz barely looks in this movie like he would when he was shooting Back To The Future.
Nicolas Cage (18) - I'm sorry, "Nicolas Coppola." He passes, but Cage always weirdly looked older than he was. In fact, he's had that receding hairline for so long I'm surprised he wasn't 50 a long time ago. Note also that FTARH has aged far better than Cage's own teen flick, Valley Girl.
The blonde cheerleader - Don't know how old she was but she passes.
The Pat Benatar lookalike - She looked a little too old.