There are many reasons why young women date older men. Just as there are many reasons why young men date older women. its fun to describe social phenomenons but more often than not each case is very unique. People tend to over simplify psychology and usually the results are entertaining speculation. But I wouldn't think twice about stuff like this.
LOL, I would like to date younger women when I am old.
I guess its cause they see a mature person in the old man. Maybe a man who may give all his attention to just her all the time is a good enough reason. An older man may be reasonably more settled than a younger one. And well women like to be with the leader of the pack, and older men are often leaders.