Older: 12 years
Younger: 14 years. I generally date younger men. Present guy is 7 years younger.
Female, straight, early 50s
For actual relationships:
Older: 4 years
Younger: 1.5 years
Male, straight, 35.
Older: 15 years
Younger: 4 years
Straight female here, 31.
As a general rule, I’ve preferred older.
Currently 41 year old woman, straight.
Was briefly engaged to man 9 years older, and for nearly two years dated a man 7 years older. (But he was mentally and physically more like 15 years older).
Age difference was part but not all reason for break up.
Younger? Ex husband is two years older than me. Lack of maturity on his part was part (but not all) of the reason for separation.
Current partner is almost a full year older than me. (For ten days a year we are the same age) and its my longest lasting relationship.
10 both ways.
Straight Male, 48
I was interested in someone 14 years younger then me, but she had too much sense to be interested.
Straight male, 40
Older: 16 years, I was 24, she was 40.
Younger: 9 years, I was 39, she was 30.
Straight female - 43
Older: 17 years - and he was the last in a long string of progressively, slightly older than the last one, men. My husband is 3 years older than I am and he broke the trend 
Younger: 1 year. I have only dated one younger man and I was in high school at the time.
Gay woman
I’ve dated 12 years older and I’m currently dating 3 years younger.
32 straight guy
Older woman: 3 years
Younger woman: 2 (I think)
Hmm, interesting. There seems to be more Cougars out there than Sugar Daddy’s.
Contrary to popular belief. 
I’ve only had 2 serious relationships. The first one, the guy was 2 years younger; my current boyfriend is 3 years older.
I’ve casually dated guys 5 years younger/4 years older than I am.
Counting both relationships and dating.
Older than me: 5 years. I was 23 when we met and 35 when we divorced.
Younger than me: 10 years younger.
Straight male
I’m one of the ones who said I often date younger men, but I don’t consider myself a cougar. To me, a cougar is a woman who is on the prowl for younger men. I don’t prowl. The younger men I’ve dated have all pursued me, and most of them had no idea how old I was. Before I started dating my present guy we were friends, and I never knew exactly how old he was, either.
Straight male, 32.
My outliers are 15-ish years older than me, and 9 years younger than me. Both occurred within three months of each other, and both were casual.
When I was single, my usual sweet spot was -5 years to +2 years.
I hope I didn’t offend you. I was just making lite fun.
No, not offended. But dating’s hard enough for an older woman without being subjected to unearned labels.