It is easy to find post hoc "explanations" for a finding you did not expect in the first place. That is not science. Science is about testing theories. No theory about the decline in sexual frequency has yet been tested. It is a puzzle. This is mine https://plus.google.com/101046916407340625977/posts/8o3isk7Nc1g …
The hypothesis in nuce: Because of the drop in birth rates, there are too few younger women for somewhat older guys.