Why you shouldn't hang out with your brother's friends

I have a few brothers. Usually far more than I want to have but I'm pretty close with them. I'm particularly close with my younger brother, and since my friends can really only handle me in small doses I don't have a lot of people that I go out with regularly. So sometimes I end up hanging out with my brother and his friends. Which is fine until you realize that the guy you've been chatting up all night is 19. Of course this would never happen with my older brothers since they still refer to me as their little sister even though they date women younger then me and we don't hang out very often anyway.