no i dont think you should make him go more....
i had the oppisite problem as a child, and if you make him go more his blatter will not hold as much making him have to go a lot!
if his blatter can hold it with no accidents, let it be....you'll be thanful on your next vacation that you dont have to stop one million times to "potty"
lol consider yourself lucky!
if it concerns you to much ask his doctor, and have a urine screening done...but i really think it is fine