How come the showing of skin on an older woman can’t be sexy and attractive?

I don’t know how many times I have heard that after a certain age women should avoid fashions that show skin like minis, halter or tube tops, Daisy Dukes, thong bikinis, etc. It almost seems to me like a tacit admission that older skin is not or can’t be beautiful, attractive or sexy. If a woman took care of her skin, exercised regularly and was toned with good skin quality why couldn’t she wear fashion or styles like that with out scorn or ridicule? Why does she have to be accused of trying to dress like a 20yr? Are 20yr old supposed to have cornered the market on sexy or seductive wear that show skin? Or is telling middle-aged and older women to avoid that is a backdoor way of saying “you have too many sags and wrinkles, you better keep that hidden”?