I guess I may be showing my age here, but growing up on the farm in Iowa was a bit different then. When I was 4, my dad would put me on a steel wheeled 10 20 IHC with a two bottom plow and get me started. He would get on a '39 "M" IHC with a three bottom plow and stay behind me (close behind). I could not trip the plow or push the clutch but my instructions were clear. If there was a problem, pull the throttle lever down and kill the engine. Of course, we were moving about a mile per hour. At seven, I drove the family car with a four wheeled wagon 5 miles to town with the grain at harvest time. I was not the only kid doing it, the grain elevator kept an employee there to hook and un hook the wagon, lift the gate, and help dump the load. At 14, I was issued a driving permit to drive the school bus, deliver the route kids on the way home, park the bus at home, then pick them up on the way to school the next day. If I remember, it was an old IHC bus about 20 passengers. I thought I was big time as those of us who were chosen got a day out of school twice a year for a bus check and driving test.
I started my sons pretty young here in California, but it was in the desert driving go carts and buggies. Wish they would have had the opportunities I had as a kid.