Well, I think for a lot of people 15-year-olds are taboo. If I was transferred into a 15-year-old body I'd be "chasing tail" and not have any problem with it (although I am only 21 now). Maybe I am a sicko.
Anyway, I don think they should have put him in college becuase they would have had to say he is a genius to get over the age issue, and although Jack is not stupid, he's not exactly gifted either (I'd say his IQ is 110-120, slightly above average). They could have forged documents that he is an emancipated senoir and put him into High School. Becuase another problem is that he doesn't have any parants, or a house or anything, and DCFS would catch on quick. The Air Force could circumvent that by setting him up on his own with a little pension and stuff.