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.