Are there women over 35 who like men in their early 20s? Sure, what's not to like?
Are there women over 35 who would DATE men in their early 20s? Yeah, though not as many. Most women simply wouldn't find someone that much younger very interesting to be around. A huge part of sex is imagination, and once you've gotten over a younger butt, what else does the guy have to offer?
Are there women over 35 who COULD date men in their early 20s?
This is probably the smallest group. For better or worse in Western society, most guys find women in the 15-30 age group most physicall attractive - so you need to have a lot more going on to catch the attention of someone if you're older.
So - Cougars are that special subset of people who WOULD and COULD date younger men - and that is a pretty small number.
I'm sure there are lots more who have tried it, but going out on the prowl once doesn't really count now, does it?