None of these answers work for me. I have always found that dating or partnering with a person within ten years of my age worked best. For me there needs to be a common experience of the world and the culture -- which can be lacking with larger age gaps. Examples: on a date with a man fifteen years younger than I was, we saw one of the movies about the aerospace industry and the race to the moon. He had no clue about any of it while my father was involved in the entire thing, so I was very familiar. Another example was when on a similar date I mentioned Gilda Radner. His blank face indicated he had no idea who that was. I'm not a devotee of current pop culture so someone much younger can certainly bring up names and events with which I have no familiarity. I have found, however, that slightly younger men often are less likely to have extremely stereotypical perceptions of gender roles. As an untraditional woman, that's refreshing and greatly enhances the relationship.
Now, at 70, I cannot imagine dating someone 90. The biggest problem with someone 50 would be, again, differences in our life experience. I'm retired. They most likely would not be. I'd prefer a partner who has time and freedom to operate outside of the constraints created by employment.
To each her or his own. As mentioned several times, each person can choose. I just think it's a great deal more difficult to have a relationship with someone two decades older or younger.

Consenting adults can do whatever they want. Not place to judge.

If it's consenting adults age isn't an issue imo

to each their own but for me 20 years is a bit too much. On the day I moved here (March 10 2018) I was seated next to the most beautiful young man. I found him totally stunning. At take off he started trembling, sweating he had the worst flight anxiety I ever seen. I held his hand the whole flight and kept him talking. We exchanged numbers at the end and I took a selfie with him. We texted a few times, but when I realized he was only 25 I couldn't go through with it. Damn flattered though. I did text him one more time a few months ago when I was on a flight to Burlington. Just to say I was thinking about him as I do every time I fly. Thomas.

I know 2 women who both married older men. One was 30 yrs. older and the other 23 yrs. older. Both marriages were good but the problem is they have recently buried both men. If you can handle that aspect of a older/younger relationship - go for it. the one told me the age difference did not enter into any consideration for her when they married.

I have known people who have done this and sooner or later it caught up with them. For me I demand commonalities and some companionship not just a sex toy.
Speaking of which I just heard a funny comment. What does a woman call a vibrator?
A toyfriend.

I look younger than my age. Seven years ago I belonged to a Singles Professional Group out of Boston, Events and Adventures. I met Geoff who was 25 years younger than me. My age didn't bother him amongst our Group. We had mutual friends who accepted our relationship. Then he realized I was a few years younger than his mother. Never introduced me to any of his siblings or family. That hurt. Never met his close friends outside our Group. That hurt even more. It became a long distance relationship as he traveled to China, relocated to California and eventually Washington, DC. Meanwhile I was diagnosed with leukemia and fought for my life. We are friends now. He remarried his wife and 10 year old daughter and I fell in love with Dan here on Agnostic. I've always dated younger men usually 8-15 years younger but Dan and I are in the same age range and are doing just fine.

My husband is 17 years younger than me, but I think the only reason it works is because he was in his 30s, not his 20s. I wouldn't advise dating with that age gap if the other person is in their 20s, they are simply not mature enough yet to know what they want in the long term.

none of the answers suits me since every single one makes a judgment based on a generality. how about if it's okay for this one and not okay for that one based on who the individuals are?

g

In the past I have dated in a range of men five years older to nine years younger. I doubt if I would find a man 20 years younger than me appealing, since my older son is 19 years younger than I am, and it would just feel weird to be with someone in my sons' age group. At my age, I would probably not find someone 20 years older than myself who would have the vitality necessary to attract me.