DY: you’re forgetting one piece of the puzzle. Assuming all other variables being equal, if a 23 year old boy has a choice between dating a 21 year old girl from a not exactly rich family versus a 19 year old from a wealthy family, whom will he (or his mother) choose?
So assuming the older rich females are no longer girls (they go fast) the boys will go for the younger rich girls whose parents promise support whenever possible. And the others are often left out in the cold. Of course other features such as beauty, yichus, smarts and what-not also come into play, but you can’t deny that money is a major factor, and those lacking it do not have a competitive edge.