BJJ Boy, with hard work and determination, anything's possible. And no, most people don't start until they're around 14-17 anyway. I mean, there are a lot of kids taking things like TaeKwonDo, but:
1. TKD pretty much contradicts everything in MMA
2. Most parents don't enroll their children in MMA classes. Don't get me wrong, it happens, but not often.
So yeah, you've got a shot. Good luck.