I think there is such a thing as too old for down hair. Kate isn't it, yet. The only thing about it is that she could end up looking a bit Real Housewives if she keeps her current style.
Meghan's hair looks very well maintained but too long, it looks very extended. (I don't know if it is).
I don't wish to be mean but Princess Anne is not the best example of an older long haired look. It makes her look like a Victorian governess, and not one of the cuddly ones. I would love to see her hair "fixed".