My 12 year old bro is 5'1 and 150, my parents took him to a nutritionist, and he said that "the boy has absolutely nothing wrong with him, and as long as he excersies, he will have no trouble at all".

So who knows. I guess though, being a guy, and him not liking girls yet, its easier for him. Only 1 kid called him fat, and got his ass kicked for it.