There's 15 years between Alan & I, and for the most part it's just a number.
I dated both directions (older and younger) before I got married and found that younger guys weren't my thing, so by the age of 19 I was pretty much sticking with guys in their early 30s. There are a lot of advantages to an older man, not the least of them being sexual.
Most of the issues that Alan & I had happened in the first 5 years of our marriage, and they were more personality-based so I believe they could apply to people of the same age as well. I'm a lot more "hyper" (as he called it) and adventurous than he is, and it was worse when I was younger. Over time though, we managed to balance each other out very nicely. I helped him release some of his repressed wild side, and he helped me curb my overly-vigorous and sometimes self destructive tendencies down. There's never been any power plays in the relationship, but then again both of us are really open-minded and have always been willing to work towards the middle ground in any situation.
Family was a big issue... both of ours hated who we were with. But we pretty much just made the choice to be with one another no matter what, and the families eventually got over it after a few years. I know that sounds selfish, but we both knew we'd found the right partner, so nothing else mattered.
Now that we're getting older, age is a factor once in awhile because my hormones are going nuts with this pre-menopause crap and I pretty much want to have sex 24/7. Alan keeps up amazingly well (at least once a day), and when he can't we compromise. He's a master at erotic massage and oral, plus we've got a good collection of toys, so we still manage to keep up the intimacy on those "bad back days" of his.