Yeah it's icky because how old he is. Old people just smell funny. How can anyone have sex with Barney Frank? Seriously. Woman or man, it's disgusting.
I'd rather not think of old people having sex. I'll just assume they are co-habitating and they enjoy each others company as roommates.
That's your reason for thinking this is wrong? Because of how an old man smells and how they have sex? Wow.
The only reason I find this wrong is because of the psychological ramifications behind it and the psychologically traumatic (not sure if traumatic is the right word, is there a word for something that has a negative impact but not to the point of trauma?) events that occurred beforehand to drive someone to a) go for someone 30 years younger than you or b) go for someone 30 years older than you.
Reasonable human beings stick to their generation when looking for romance. At what point does "Hey, this guy is thirty years younger than me, I'm old enough to be his dad. Seems like a reasonable candidate for a life-long commitment." seem like a 'normal' thing to say?
Besides the fact that one is going to die far sooner than the other (life span wise), there are also these things: radically different health concerns due to different age bracket, generational split, the inability to have a healthy relationship (if you can't get someone in your own age group, perhaps reconsidering your life is a good idea), incredibly different libido and sexual capabilities, financial strain (one will spend the majority of their marriage in retirement), and, well, social scorn.
There are some evolutionary explanations for going after older people, but most are primitive (which, by the way, we humans like to claim we're not, so let's act like it, hmm?). Women go for older men because older men are generally more geared for protecting them and providing them the foundation for a stable life (which means nil in modern society, not to mention that nowadays a 20 year old woman is likely more geared to protect herself than if she held her 50 year old boyfriend in front of her to take the shots). Men go for younger women because younger women are generally more geared for having a child. Living in a society where there are countless orphans and abandoned children, you're better off going for adoption if you're 45+ and suddenly want to have a child.
Having a son and daughter isn't only genetics. There are other factors involved. There are exceptions, but people who have children late generally tend to be worse parents because they lack the inspiration and physical capability to keep up with their child, especially if they still have to work. My blood line has a bad habit of having children at an old age (in fact, my parents had me very young, all things considered, my mother was 30.) and as a result every single person I have met that I am related to is a giant douche because their parents never gave an actual damn about their road to maturity.
Again, there are exceptions to this. However it doesn't change the fact that all "evolutionary advantages" going for older/younger people are outdated and no longer applicable. You will end up having a healthier relationship by being with someone in your own generation. There are many social, cultural, and lifestyle differences between these two men that I doubt their relationship will last long, or be particularly helpful towards their mental health in the long run.
Either way, I can't force this down someone's throat. I don't care if they do this. There shouldn't be a law against it. But it's still weird given the circumstances we live in.