My neighbor started really early with his 4 years old boy. He bought him a Power-wheels truck and made a trailer hitch for it. He has a flatbed trailer he can tow around an pick stuff up....He's gotten better than Dad at backing that thing into tight spaces!!! (and Dad's a semi-truck driver!)
I remember learning all the RV'ing stuff at an early age too. It was always a privilege when Dad let me turn the crank that raised the roof on the old PUP. We all had duties in the family when it came to setting up or taking down camp, and we rotated for each week, so we could each get experience with the operation. I didn't get to drive the rig till I was about 14 or so, but Dad definitely had me checking tire pressures, and hitching/unhitching whenever we went somewhere
My kids are 7 and 4. My son drives the tractor and 4 wheeler while sitting in my lap, he has also drove the truck too. I do have the advantage of having the same farm that I learned to drive on still in the family and nearby. They also help me put the jacks down and setup camp. My daughter is very eager to help also just not quite big enough. They do fight over who gets to put the jacks down so it is usually 2 a piece.