You don't hear as much about what I refuse to call "cougars": women substantially older than their male partners.
Could it be that men prize youth and beauty more highly than women do?
Well, if you're 50 and your companion is 70, you're almost bound to provide care long before you would for a mate of the same age. Plus, most people would willingly choose to endure the rough patches so long as they get a reasonable run of the good stuff beforehand.
Your children, of course, may not see the lure of September-May dating quite the way you do!
The older person, for his part, gets a higher-energy companion who is likely to help the couple stay fit — and, quite likely, more sexually active.