It's ok for any man to divorce their wife and marry a younger and prettier woman.
Legally, in most places, yes, of course.
Morally it obviously depends on the individual case, but if we're talking about a general trend then it's not a great look to abandon wife (and possibly kids) in order to 'upgrade' to a newer model, particularly if this is based entirely on physical appearance. People aren't cars.
And I think that's shallow — giving up and quiting on your relationship with your wife just to be with someone "younger" and "prettier". Some men may be like that but I don't think it's fair for the wife especially when she'd gotten old and tired because of taking care of her family — including the husband of course. I just feel bad for those wives who're left behind instantly by their husbands, especially when they already have kids.