My daughter is 13 and still loves dolls (right now she is in an "American Girl" phase, my son is 11 and likes to play with his "action figures" still. There was some study done that shows that boys will make other objects into toy guns. I guess its in their genes.
It's comforting, in a way, that boys will naturally do this. I remember when we would play my little brother was always there "shooting" the bad guys. Always made me feel a little safe, even if it wasn't real.