Am I the only person in the universe who doesn't think they look too young? I mean, they're only supposed to be in their 30s/40s. I have a 36 year old philosophy teacher who looks like a GQ model, and my 30-something Sunday school teacher is dating a guy in his twenties, she looks so good… so I'm not seeing the Ghostbusters looking too young here.

-Graves

I have no problem with the age of the characters; partly it's a stylistic/detail thing, and partly because E Graves is right. Appearance isn't always an indicator of true age (would Peter be vain enough to use hair dye? I think so!), and the actors didn't really look THAT old in the movie - the sort of detail you'd want to use in art would slow down the drawing process, and perhaps clutter their faces somewhat.