When I was 18, I married my 22 year old BF...the only gap was that I was way more mature than he was...HEHEHE!!!!
This should not even be an issue.
My husband is 7 years my senior and that's just about pushing it for me. Also, my sister is married to a man that's 7 years her junior and she said the exact same thing...any more and it would be too much of a difference! IMHO!