Why do some older folks call legal adults kids?

You have a fair point what your saying is true. However I am 23 and I have no problem being called a kid or a girl, even though I'm an adult and a woman I still feel very young and I don't find it insulting unless it is said in a condescending manner. I'm still in university though, and I think that if I was in a working environment I would find it insulting. In general I don't think people mean to be offensive it's more just that they feel at that age they were so clueless compared to how they feel now.