7 and a half years difference between me and my gf. Im 28, shes 21. Get on great, I'm a childish retard and she is mature and sensible. We bring each other up to each of our levels and balance each other out. Having the same interests helps. The only thing we have slightly different really is she likes r'n'b and I like metal but we both like rock, folk and most other music. Films, games and hobbies we are the same.
As long as your both of legal age it shouldn't matter as long as you really like each other and have lots of fun together.