I don't have a problem with people in their 80s having sex. I think they're both intelligent and interesting individuals, which is an attractive combination. I can also see her deciding at this stage of her life, money is as important as love and affection. Although she's wealthy in her own right, he can offer her an amazing life style she would enjoy. I can also imagine him being very loving toward her (and the rest of his family).
Maybe sex isn't on the agenda, who knows? But I still can't imagine them having sex, so I will not do it.