I might like my best friend's younger brother?

I think there is a good chance he does like you. You are older and more mature than him, and that tends to attract young boys his age just as they are getting into puberty. As for the age difference. 3 years isn't too much necessarily, but is generally considered pushing the limits at your ages. When you get older, the age differences don't mean as much, but unfortunately, 3 years difference at that age is quite a lot. Plus, it is your friend's brother, so that is always weird. If you are serious about it then the best thing to do would be to ask your friend. If she is really that good of a friend to you, it will be worse if you don't ask/talk to her first. Not that it should be a deal breaker, but in my opinion it would be a little strange for a high schooler to be dating someone in the 6th grade. That would definitely not go unnoticed near me...