It just seems slightly unclear to me in the movie whether they're in a high school or a university. I know that it's supposed to be this CalTech-esque thing, but the movie itself seems a little unclear with the presentation, you know what I mean?

I don't think it's particularly unusual for 15-year-olds to have sex, but Mitch is indeed a nerd's nerd and in no shape to be having sex during the movie timeline.

*g* Not to mention that there's just no way I would write 15-year-old sex. Just can't do it! Even writing him (once) as 17 made me feel uncomfortable.