My boyfriend is 11 years older than me (22/33). I actually asked him again last night what he thinks about the whole age thing and his response was...um, you're still more mature than me.
He's more apt to going out and I'm more apt to cooking dinner and watching a movie at home.
An issue that could arise is that of children. I assume (I could be completely wrong) that you may want to have children, whereas an early 20-something may not want that at the current state in their life. Big issue for some people...