I found the age difference creepy

Good point. He really didn't look that good. It was one of his last movies and I think Cooper was already probably sick.

But he played a very rich and successful businessman. And these things happen all the time, although they don't usually last that long (Hugh Hefner, anyone?).

I absolutely agree about Cooper in Love in the Afternoon. He seemed ill and very old.
There were many fifties' films that had the theme of an older man and much younger woman being interested in each other. As a young girl growing up in that era, I loved most of them because I put myself in the younger woman's shoes. Now that I am older, I realize that there were fine actresses who no longer worked as leading ladies beyond the age of thirty-five because they were considered too old for men who were about their age or even older. If they didn't want to accept the "character" parts they were out. Many returned to live theatre where such blatant discrimination was not so evident.

Age difference issues depend on the person and his/her idea of what is acceptable. I have relatives who married spouses with 30+ age differences. They were from a foreign culture where who you marry matters more than the age of the spouse. Some people are ready to marry at a young age while others take a longer time to "settle down". Many times, socio-economic reasons play into your spouse selection. I think compatibility and shared interests and goals are much more important in a relationship than age. Divorce rate was reported to be around 50% and I do not think that a high age difference is the reason for such a high percentage.