Lol.....you should hear what he says to his friends when you're not there. Guys are guys and we often keep our 13 yr old maturity levels around the guys. You dont know that?
He just got caught. :). Call him on it and see what he says
Specifically though, Some do some don't. Usually Its guys who aren't used to dating Alot of beautiful women...so I guess you could say it's a form of inexperience not immaturity. If women knew half the stupid crap we do or say around The Guys, we wouldnt get any dates.