I can answer this question with a fair amount of experiance. I am 27, my husband is 51. We've only been married about 5 1/2 weeks, but we've been in a relationship for almost 3 years. For us, it has never been an issue. We have zero desire to be parents, it is a first marriage for both of us, and we have a lot of interests and hobbies in common. We are inseperable, neither of us really opts for "girls or guys" nights out very often, even.
I fully understand why some people might object to a May/December marriage for themselves, and might think they can imagine drawbacks, but I find it very offensive when someone might call it emotionally unhealthy. It is emotionally unhealthy to shut yourself off a life partner for reasons out of your control like age, race, hair color, etc. The heart wants what it wants.