Apparently, all you have to do to make the thirtysomething star of your film look high school/college-aged is to comb their bangs down as far as possible.
THE TRUMAN SHOW
THERE'S SOMETHING ABOUT MARY
This rule does not apply to women, or at least not to Romy and Michelle:
I was all set to include Dexter in this as well, but couldn't find any images of Michael C. Hall playing the college-aged version of his serial killer. (And it's a TV show, but whatever.)
Which ones did I leave out?