Young brothers girlfriends

Why is it that when many young brothers have girlfriends their big brothers or sisters fear this and when the big brothers themselves have girlfriends even then they fear their little brothers or sisters.why is this so?

huh? I have a little brother, and he's like my surrogate son. I suppose it's because we are protective of them, and unlike our parents, out knowledge of the world is far more realistic, so we have more relavent concerns for their welfare...

but your questions is a little, ummm insensible

I think it depends on the older sibling. my sisters not like that. infact she only just found out I have a boyfriend and she isnt protective. she just teases me. but if your parents dont know who else is there to protect you. most of my friends dont tell any family members. but I dont understand the last bit