Lottastrikes, just wanted to say first of all that you are very blessed that your son wants your words of wisdom! I know how honored that must make you feel.
Doesn't GW have some creative writing classes? Perhaps, even if he doesn't get a minor, he could fill in with those and work on his writing that way. Another option would be to get a degree at GW and then plan on a master's in screenwriting.
Here is an interesting website. It's the winners of the Academy of Motion Pictures Arts and Sciences Nicholls screenwriting fellowships.
2008 Nicholl Fellows | Nicholl Fellowships in Screenwriting Competition | The Don & Gee Nicholl Fellowships Program | Academy of Motion Picture Arts and Sciences Of the 6 winners, 2 appear to have undergrad education in something related to film (1 of them at a community college), 2 have MFA's, and 2 don't mention any formal education at all. So there you go...