It's really a "common knowledge" kind of thing. I'm certainly not an expert on the subject. Just from my experiences with my friends and my personal observations.
As for myself, I don't date older women. When I see a girl in her mid to late 20s, and especially older, there is about a 99% chance that she's been divorced at least once with at least one kid, and she's lost her looks.
This is just my opinion, but in their late 20s, women really REALLY start to lose their good looks, and the process only accelerates from there.
It's like the stock market. Generally speaking, with age a woman's stock goes down. Also with age, a man's stock goes up. Everybody knows that.
:)