Most Helpful Guy
It is not too much of a gap per se. How it would work depends upon the relative maturity of the two partners and the extent of their shared interests. Of course, if the male is the older partner, many people will assume that his interest is only sexual, so you need to be able to withstand such uninformed judgments.
Most Helpful Girl
I'm meh on it since you're not 21 yet, but you're an adult now and you hve to learn to make your own good decisions.