Tommo's good catch was that respondents tended to discuss marriage with that big of an age range; OP only asked about dating.

Just for dating, I cannot even see why not - I do not understand why the question is being asked. For marriage, sure, there are issues of health, frailty, the woman's ending up alone in her golden years, and a host of others, but OP asked about dating. So...

-- yes, it is OK, and I regret not dating a particular guy who was 20+ years older than me when I was in my early 20s. I regret marrying my age peer instead. The older guy is a much more interesting person. Note that I regret not dating him - I do NOT regret not marrying him. He has made quite a name for himself and a large following and did eventually get married, but quite late in life; I am FB-friendly with him but I no longer particularly like him or his work, but when he was young (40+ is young), he was intriguing enough and his work back then was stellar (he is a public person and by work I mean what he says on TV). So I only regret not dating him, because back then dating him would have been a very nice and age appropriate experience for me; I do not regret not marrying him. I do not rrrrreally regret, though, as I love the son who was born in my marriage to an age peer, but since you asked for why's and why not's, here is my vote for "go ahead" with this and play it by ear.