I have a theory (I'm sure based on something I've read) about age and dating. I'm probably being dumb and obviously it requires massive generalisions but here we go...
I think the general thing is young women often want slightly older men (maturity, wealth, more ready for commitment) so a woman in her mid 20s can be attracted to a man in his 30s or older, possibly even more than she'd be attracted to a man her own age. Obviously this is a theoretical generalisation thing and not anything to do with individual people! So men in their late 20s to early 40s can actually be quite attractive to women in their 20s, even if those same men actually struggled when they were in their 20s to attract a woman of the same age.
So basically, evolutionarily speaking, men prefer youth (health, ability to have babies etc, taking from an evolutionary perspective only), so will, regardless of their own age, often be attracted to women who are 20s and early 30s. Women can therefore from 18ish potentially attract pretty much any age man if she wanted to (again various other factors but point is age is not an important variable). Whereas men in their early 20s may actually find attracting a woman harder as he wants one his age but a lot of women his age may be looking at men a bit older. But as we all age, men in their 30s are suddenly potentially attractive to women in a much greater age range than ever before (say 20 - 50) whereas as we women approach our late 30s and 40s we find ourselves in a similar position (but reversed) to young men where men our age and younger are able to attract both younger women and women their own age, and maybe statistically lean younger.
Women in their 20s = potentially attractive to all men
Men in their 20s = attracted to women their age but may find it hard as those women are looking at slightly older men
Men in their 30s and 40s = suddenly potentially attractive to both older and younger women
Women in their late 30s/early 40s = attracted to men their age and slightly younger but may find it hard as those men are looking at slightly younger women.
DH and I have been together since our late teens and during our twenties I would get approached a lot and he didn't really. Now how we look hasn't really changed much except we've aged, we're late 30s now but I get much less attention and generally only from older men, whereas he often has younger women chat to him if he's out for a drink or something. It's just definitely something I've noticed. I guess there could be other reasons (confidence?) but now I've made a neat theory haha!
Hugely long winded sorry but basically I don't think you need to feel like an old fool or anything, I think things just shift as we get older and it can be a real surprise. I think things even out again as we get into our late 40s and 50s onwards. You're not silly at all it's just all a bit of a mind fuck.