I'm almost in the 65 or older group, and I think I might be a trophy husband. My partner is 21 years older than I. When we met, I was a 20 year old model and dancer so I was in pretty good physical condition.
If two people like each other, go for it!
Usually, people with a dramatic age difference don't have a lot in common, however, my partner and I have a great deal in common. Sex with each was never part of our relationship but we were good friends.
My partner is young at heart and I tend to be an old soul. I had several friends in similar situations. Some of the situations (I think) were strictly an older man keeping a younger man - who was hoping to inherit his partner's money. My partner and I were on fairly equal financial terms, and I tend to be a tightwad with money so I'm usually the one complaining about spending money.
We have an understanding that I will make sure he's comfortable at the end of his life, then our investments will be used to make sure that I can afford the care I will need to make sure my own last days are comfortable. Once I die, the sister and niece of my partner's ex will inherit my estate. The sister and niece have been like family to me, I'm happy to make them my beneficiaries.
If an old fart and a young stud WANT to be together, why not? Chances are slim, USUALLY, but it does happen from time to time. I think what weirds people out is the pictures they have in their heads of sexual situations. You don't know for sure that sex is even a part of their situation - if it is though, to each his own!