I don't think the two things have any connection at all. To say that little kids dressing like "tramps and thugs" = little kids dressing like teenagers is wrong. Not all teens dress in that manner and to say that they all do is very wrong.
I was a little old lady when I was a kid. I still like cartoons (preferably Beavis and Butt-Head). I would rather wear jeans and a t-shirt than a dress or suit any day. I despise being called "Ma'am" as it is a contraction for Madam, which implies a married person. I don't like the assumption that since I am on the other side of 25, I should be married.
I was just reading Cher's bio and I think her experience is somewhat typical of a lot of women. She married very young and then divorced and discovered all the things she missed. I guess Miss M finds it distasteful that 40 year old Cher dated a 22 year old man who is one of the hottest things I've ever seen. I doubt that she would have a problem with a 40 year old man dating a 22 year old woman.
in other words, I think Miss Manners is full of shit.

There's nothing wrong with looking 40 when you are 40. There is something wrong with looking 40 when you are 25. This was epidemic in my hometown - I was the freak as I was 24 and still not attached - which is why I got the hell out.