I was in my 30's in the 1990s, and a large age gap was not considered normal back then at all! In fact, since I have been aware of what large age gaps, or being homosexual, etc, actually means - from the 1970s upwards - there has been a much greater acceptance of homosexuality, but no noticeable difference in how well large age gaps between couples, have been tolerated.
Homosexualality is, and probably always has been, a natural part of nature. I say "natural" because there have been many occasions when animals other than humans - have been both observed, and recorded, behaving in a sexual way with other animals of the same sex and genus.
Although on the face of it, sex between two animals of the same gender does seem unnatural, because reproduction of a species cannot happen in most animals if they are both male or both female, I don't believe it would happen at all if there was not a good biological reason for it. Perhaps we humans might just not be knowledgeable enough yet to understand what the benefits are, and unfortunately, this is not the right place to start pondering about that!
Large age gaps between human couples are probably still frowned upon for the same reasons that homosexuality was for such a long time during our history. That being again, because of the dangers of the female of the species not being able to conceive at all, or to conceive a healthy, viable, baby, outside of some quite limiting parameters. Although adult men seem to have a longer period of time in which they are fertile, there are many ways that the quality of their spermatozoa can be adversely affected, and reaching an older age can certainly be one of them.
So, HowBizxarre, where you were brought up, 31 odd years ago, may have been more open to what people of my age, and my parents age, would have often considered inappropriate age gaps, and would have therefore batted a lot of eyelids, we are now, hopefully, more practiced/educated in the rights of consenting adults, who harm no-one else. Where we once might have sadly looked down on such couples we now thankfully know to mind our own businesses 🙈