Age is one of many many factors to consider in a relationship. Personally, I know a friend who was in a relationship with her same age boyfriend (both started dating while they were juniors in college) for 2 years and they are absolutely miserable with each other. I also know my aunt's herb doctor whose wife is 10 years younger then him, and their marriage is very blissful.
People, instead of focusing on age, should focus more what they have in common with their partner. Do their interests, values, and outlook on life mesh or are they in conflict with each other? I believe this is more important and can make or break a relationship no matter how much age difference is there.