What should the maximum age difference between partners be?
I've always heard of men having a formula to determine who is too young to date:
Your age, halved, plus seven.
[(Your Age) / 2 ] + 7
For example, if you are a 34 year old man, half your age is 17. Add seven to that and you arrive at 24 years old. A 34 year old man can date a 24 year old woman and not raise eyebrows. A 23 year old? Too young.
Another example: if you are an 18 year old male, half your age is 9, plus seven years is 16. If you're 18 and in high school, don't date any freshmen girls or you will be seen as a creep.
So the maximum age range fluctuates and is dependent on the age of the two people involved. Obviously, as someone gets older, that age range can grow larger and still be within social norms. And a 15 year age gap when you're young may be a bit much, but later in life when the couple is elderly, it matters little.
But let's figure out the maximum. Let's say there's a 100 year old man on the prowl for a younger woman. Half his age is 50, plus seven years, is 57. So he can't run out and get a crazy stripper wife. The age gap is 43 years, and I would deem that to be acceptable. But if it were a 65 year old man dating a 22 year old woman, the age range of 43 years doesn't apply. That's why we have the formula that takes the man's age into account.
I suppose it works for women who are dating an older man. They must fall within the formula's age range or suffer the possibility of being labelled a gold digger.
As for older women dating younger men? I don't think there is much of a social convention. It may raise eyebrows, but say it's a 45 year old cougar dating a 23 year old male model, no one really cares. As long as the woman is not engaging in statutory rape (like a school teacher going after boys), people don't care. And even then, some guys think it's kinda cool that there are 14 and 15 year old boys nailing their hot teacher.
So there is a definite double standard for the genders. But abide by the aforementioned formula, and you will be fine.