Actually, I think critic above had it right. Sure, women are considered more attractive when 20-30, and get a lot of attantion from men in that age, much more than men do at any point in their life. After women get past 30, things simply get back to "normal", but to them this seems as a shortage. In fact, single women above 30 seem to be the only group that ever refers to a "shortage of suitable males" - in my experience, younger women and men are generally surprised as to why such thing should ever exist.

Furthermore, the theory that men are trying hard to marry, and the most attractive ones "succeed" to marry at a younger age, just does not seem to be realistic, especially not in modern society. There are good reasons for men not to marry early.