that's way too young to be doing that
but by your own words here. you are implying there is an age where wearing super short skirts IS ok.
so if its ok for some people and not others. where are values decided as to age then? certainly not by you if you are against it. but who? because unless there is some majority concerned about it, its not really an issue. and if not majority, then not society.
you see how this works? its social evolution here. you can dislike anything you want, but its a far cry from what is right or wrong.
does pop music = girls wearing short skirts? maybe.
but this does not indicate that wearing short skirts = bad. thus age would be irrelevant.