I think, the time you might find a decent man is probably early 20's. Unfortunately, as a woman in your early 20's at the time, you don't know enough, read all the signs. I doubt the young women who found good ones were any better at it, just luckier really.
By the time you get in your 30's, the good ones have gone as no woman with sense is going to let a good one go. The ones left are the ones who either keep getting dumped, do the dumping because they have FOMO on others so can't commit to anyone, or have behavioural issues from poor childhood experiences - drugs, alcohol, violence, abusive etc.
I do consede, that on a rare occasion a decent man may find themselves single at an older age, because they maybe made a poor choice in their 20's. However, they are in the minority as, being decent men, most are still likely to stick with a partner who is not ideal if children are involved. Like most women, decent men will put up with a lot that's not right for the sake of their kids.
Hopefully, this means that there may be a few more decent men around in their late 40's/50's who stuck it out until their DC's became independent. They are hard to tell from the same age guys who got dumped by their wives for being shit partners though and likewise stuck it out till then for the DC's.
So maybe, it would be reasonable to ask an older man you date, who has come out of a long term relationship, who ended it? If it was their ex, she was getting rid of a substandard male, so perhaps be wary , there were probably good reasons for her to dump.