An age difference between two partners can be a difficult thing to overcome. Even if it is a small one, like a year or two, it can feel like a chasm, depending on where you are in your life. But if it is large, surpassing five or even ten years, it takes a lot of work and determination to stay together. Both partners must actively work to understand the other, because no matter how much one wishes to deny it, they come from different times.
Sometimes, however, there are two people who are just so made for each other that they cannot help but be together, despite their age gap, and that's a wonderful thing. Because who's to deny anyone happiness? If people can find any sort of happiness together, then they should be let to live without being judged for something so trivial as age.
The taboo around large age differences is ridiculous, because there is more to maturity than the number of years you've been alive. There are life experiences to be considered, and personality traits to be analyzed. You cannot look at an individual's age and be able to tell where they should look for a partner. It's not rational, and it's not possible.
Let age difference be a problem the couple has to tackle, and just enjoy the fact that they're happy.