There is no rule. Of course, I never liked to follow them anyway. I have seen large differences work, and no difference not work, as well as vice versa. I think I actually have an undeserved wrap as being a cougar type, due to the large numbers of males 10+ years younger than me that seek my company. They seek me, not the other way around. Honestly, it is men closer to my age and older that pique my interest more. Not to say that the younger ones do not or can not, just less often, for reasons not unlike what Raev listed. There are many males that have years on their side, but are less of a man then their younger counterparts. There is issue with the older as well. I have dated much older, believe me, they didn't look it! The problem was differences in interest in social activities. Partially due to age difference, but I am sure not an issue with all, as different people have different interests. More important than numerical age, is the person. For me, if they have their shit together, drive me crazy in that good way, make me feel like I should be made to feel, and we enjoy each others company, then what the hell does age have to do with it?