At 20 I met a man who had just turned 37 and we fell for each other literally overnight. Not because we had sex, but because we spent all night talking. I was a good student in school who preferred hanging with the teachers asking questions after class to goofing off with my classmates. We were together for 9 years and then I lost him to AIDS-related encephalopathy. During those 9 years he helped me get an education and we bettered our careers enough to buy a house together. I miss him still.
Not every May-December relationship is as healthy as ours was, I admit. But don't assume they are all unhealthy, either. Find out what brought them together, what keeps them together, and what benefits each one brings to the relationship before judging them. As long as the younger man isn't being damaged in some way, I don't see what the fuss is about.