I understand the perspective of most (not all guys) who prefer youthful looking women, I mean. Nowadays, wake up, with all the media attention about the hottest girl in the maxim or gossip magazines. Most girls who going through extreme levels to try to keep into shape even after their 25's and later age.
This puts them into a different class where most (not all girls) will find it hard to compete with youthful girls, such as 19/20. Honestly, 6/5 years does means a different to a person, whether its hair, skin, wrinkles, teeth, knowledge, etc.
We all go through the aging process, men and women aren't going to stay youth looking whatever. As for men, (most, not all guys) work to produce. Most of women (not all women) are housewives, or later in life that is, they won't be able to reach their potential due to caring their children. Like again, there is a few exemptions to everything I said, they'll be single parents, women working independently and men being the house do-er, etc.
What I'm saying is, there is a massive stereotype and generalization, people make. e.g. If your an investor, like me, you'll notice, Board of Directors in most company nowadays for multinational companies are made up of men. You should ask them, why?
Anyhow, final point, its not women market value that goes down, sometimes its up, vice versa with men. I've seen men who doesn't take care of themselves or do stupid things and get up with two front teeth knocked out or no hair whatsoever or beer belly.
So frankly I can see lots of arguments throwing at different sides. All I can say is the OP made a generalization, rather than statistical facts. Now I much prefer to go enjoy myself in the garden rather.