My last partner was 20 years younger than I. We were together for 20 years. It was the most wonderful 20 years of my life, but I was realistic. Eventually, he would want children, and when he started mentioning that issue, it was over for me. I set him free and we are best friends today.
There is an acceptable and realistic age gap for a successful relationship. I read recently,that people closer in age have a greater chance of success. Personally, I have always been attracted to older women and have had three relationships with older women ranging from 8 to 13 years in Difference. In two of them,we simply wanted different things out of life. In the third and longest relationship we were simply at different stages of our life, I was 22 she was 35. So, my take on the age game is that its complicated and there is no difinative answer to the question.
Age is just a number, but I would feel strange dating a man my adult kids's age or gasp, my adult grandson's age. It's been my experience, having been hit on by dozens of younger men, they are only looking for a fantasy with a sexy older woman, not a love relationship.
As long as the male is over 21, my guess would be whichever age gap is comfortable for both parties. I once had a crush on an celebrity who was 20 years my junior but it was safe.....he never knew! Realistically, for me, I would be comfortable with a male no younger than 10 years my junior....as he would have experienced much of what life has to offer him.