I have had relationships with people up to 22 years older than me, and my current partner is 17 years younger.
I was reluctant at first, but he initiated the whole thing, and insisted it would be right, that age didn't matter. He was right.
Harold & Maude really puts it into perspective
(Another great couple, Edith Piaf & Theo...true love to the end.)
The thing to take into account is vulnerability, as there are those who would take advantage of younger persons to boost their egos, while the younger person is assuming it's deeper than that. This has happened to me, as I was very naive. (I still am, so it must have been extreme back then).
An older person should stay above 21 though, nothing younger than that, and even then, make sure the younger person is initiating, or is very mature and knows what's what (probably necessitating that they be NT, therefore).
And as scubasteve says, "In your early 20s, it's really much simpler than that... 18 is the lower limit."
My conclusions...It depends on who is initiating, and what their motive is.
Ego is a bad motivator....sleazy older people, no way, but if it's genuine Love, fine.
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AS 169/200
NT 23/200