Age gap problems?

So I'm 17 and my boyfriends 21 I will be 18 at the end of next year and he will 22 at the start of next year! I don't see the problem? I have never had anyone say anything to me or him about it and my parents and his are fine about it! I'm quite mature for my age and don't have many friends my age I don't tend to do what normal 17 year old girls do anyway and I see my self as a lot older as it is. But what do you guys think honestly? I would just like to know! I do really like him and I would have never chose to fall in love with someone that much older but I have! What should I do?