My Dad was a commercial New Bedford Fisherman and my mother's brothers were both Master Captains by the time they were in their 20's. My grandfather owned his own fleet which was run by his sons, and his father before him was Asa Thomson - one of New Bedford's Master Shipwrights of the 1800's.
My 14 year old son is a competant boat handler, although his mother can't seem to get the hang of "things that steer from the back instead of with front wheels and have brakes".
And, my 21 year old son was confidently operating a boat when he was 12. He is proudly serving aboard the big "PRISE" (USS ENTERPRISE CVN 65) currently steaming for the Meditranean Sea. Keep him in your prayers (if I can say that on this board

So, I think its in the blood, although I'm not absolutely positive if its nature or nurture.