My husband is nine years younger than me. We've been together since he was 26 and I was 35 (it's ten years later). It's much more common for the guy to be older, but I think it's kind of cool that our age difference hasn't caused us any problems (except in the music arena -- we're generations apart!).
The thing is, we have such a great time together we don't really think about the age difference. Sometimes I worry about what it will be like when I'm a mature, semi-wrinkly 55 and he's in his so-called prime, but life is too short to waste on things like that. He's my best friend and I hope he always will be.
The old cliche of 'age is only a number' is spot-on here. What matters is compatibility, empathy, love.