I don't think that's it (though its a part of it).
I think a lot of men and women realize that there is a lot of variety out there and people willing to satisfy their carnal desires, as well as emotional ones.
With this variety comes a lot of choice. I think there is a large reluctance to bear a portion of the emotional burden of the partner ('emotional baggage'). Men and women know that, when dealing with a potential mate with a lot of baggage, it's probably easier to just find someone with less baggage (and therefore less a burden to bear).
As a general princple, fewer years on earth means less opportunity for this kind of baggage. I know there are 17-year olds with a ton of baggage, and 40-year olds with relatively fresh outlooks, but those are exceptions: more years means more experience, which means more fatigue, which means more baggage (as a general principle).
It's a form of dead reckoning, but I see it in my own life. Women at age 22 have much less baggage than women 32, who have less baggage than women who are 42.
A bias for youth is a good threshold matter to filyer out potential mates. It's not 100% accurate, but it's a good start.
Absolutely....I sure wouldn't want a guy with "baggage",regardless of age.But I can tell you from the bottom of my heart-I could no more be attracted to a 25-year-old (someone with whom I have absolutely nothing in common) than I could a robot. Gimme a guy with a little grey at the temples (or,in my husband's case,a high,tight grunt haircut-all silver),some smile wrinkles and a twinkle in his eye that lets me know,hey,I might have a challenge on my hands-any day of the week.
And I can tell you-I am old enough,and been around enough, to have ditched MY baggage YEARS ago.
As the saying goes-there may be snow on the roof, but the furnace is cookin'!
And it isn't all about sex,either.If the little twit is too stupid to know anything about life,hell,he's just wasting my time. I think the same goes for guys and younger women.