Spider-Man is kind of a special case, though. It's pretty much an essential part of the Spider-Man universe that the main character and all his friends are teen

Spider-Man is kind of a special case, though. It's pretty much an essential part of the Spider-Man universe that the main character and all his friends are teenagers, so if you're going to make new Spider-Man movies you have to start over with new actors every few years. Tobey Maguire was (IMO) the best movie Spider-Man, but he's 47 now -- it'd be hard for him to play a high school/early college student. :-) Contrast with something like Batman, where the main character isn't any one specified age. You could probably get away with a Batman who was anything from mid-20s to mid-40s, or maybe even older.