let's see, i learned to back a bumper pull when i was 15. with a tractor and grain cart during wheat harvest. between dumps from the combine, i started just backing randomly around in the stubble.
i really learned to pull the next summer with gooseneck stock trailers hauling cattle. but i didn't start getting good in the backing department until i was probably 22. now at 25, with just a little room, i can put a gooseneck where ever i want it. i still don't like backing bumper pulls, but can get 'er done.
i work for a trucking company now, mechanicin', and while i don't have my CDL yet, i'm moving trucks and 53' trailers around the yard with relative ease. hell, i can even back them into the bay of the shop.