Young Japanese Girls?

Why do Japanese girls act so young and so cute? I would like to know the appeal, is it some simulation of purity? I find it a bit too sugary and forced, though they seem so sickeningly happy all of the time. Is it all just a show or are the younger girls just brainwashed and have no real independence? Also, how are the older women, and when does this "cuteness" stop? I realize they are often more polite than most cultures but between dressing up as maids in coffee shops and squealing at cute objects they seem to have taken polite and pure a little too far.