In general:
If a man in his 40's can get a a 25yo woman, good for him! Enjoy the sex, have fun while it lasts.
If the same man is getting with teens, that is kind of nasty and taking advantage of youngsters.
Generally twentysomething women get with older men for novelty, the money or because they did not find a compatible guy their own age. The novelty chases just want to try an older man and get tired of it after a while, a nice opportunity for a single man to get some younger azz. He might fall in love, but she won't want to commit so it's a short term thing. The golddiggers will want to commit, but once they got the ring, they have old dudes wallet whether they sex him or not and whether they divorce or not. If a prenup is in place they will stay married and keep sexing him, but she can still cheat with the poolboy when he is at work. Don't expect a golddigger to be loyal. Hence my advice to enjoy the sex while it lasts and see it as a temporary pleasure in 99.9% of the cases. Exception are people who have extremely uncommon interests who want someone who shares that and close an eye to age because of that. Say she wants someone to brew medieval beer with, do bikram yoga and travel to Myanmar, who is a libertarian and taller than her 6'2" and you happen to be that guy she'll probably not care you are 15 years her senior and still be loyal. Personality is a whole lot harder to replace than wallet or rock hard abs and big dyck, so when you bag a chick with your persona, she will be much more loyal and the relationship will last longer.
The younger the people involved the more age is going to matter, 17/25 is a bit odd while 27/35 is pretty normal and no one would blink an eye to 37/45.