I could see my youngest grandson being capable of that when he's that age. He turned 3 this summer and aready he can start the boat, back it out of the boathouse, navigate to the other end of the lake and through a narrow channel. Mind you, he needs both hands to move the shifter and has to really lean on it to throttle up, but most kids his age just put the boat in a tight circle if you let them take the wheel. I guess some kids just "get it" from an early age.
If he could open the boathouse doors and untie the boat, I'd be in trouble.