I would say that it is a woman 10+ years older and the man is 18-25.
Ballpark estimate:
Women >_ 40 + man < 30.
It's a good starting point for a discussion, though I would call some 30 something women "cougars" in the right situation. I'll get to that later in this response.
I don't fault men 18-25 for going for an older woman in the short term. Things are competitive for women 18-25. Being "older" than any particular woman helps and at 18-25, there are fewer women who will be younger than any given man. When a man is 21-22 and at nightlife venues, there are not many to be many younger women.
By the time a man turns 26, there are enough 20-25 year olds who are younger. That's a good time to focus on them and start ignoring older women. I don't think a 26-29 year old man who is dating older women is using time well.
The majority of 30 something women are not going to go substantially younger for a variety of reasons. If a 33 year old woman has a 20 year old boyfriend, she's a cougar despite being under 40.
There are enough women look really good in their 30s. It's easier to look good as a 30 something woman as a childless woman. I felt physical attraction to 30 something women way when I was a teen/early 20s guy and I feel that way now that I have turned 40.
When I was 21, I felt that the women on my college campus were more attractive than most of the hot 30 something women out there. I wasn't prioritizing hot 30+ women then but I realized that they existed. At 21, I had more access to hot 18-23 year olds on campus than the hot 30 somethings.