Assuming you are not severely disabled, you have to be 17 to drive a car on the public highway, and 16 to ride a scooter less than 50cc.
Yes you can have off road driving lessons before you are 17, and the CBT is compulsory for the scooter.
Impossible to tell you which insurance company is the cheapest - it depends on the vehicle, where you live and too many variables to hazard a guess.
Look in your yellow pages for local driving schools that give off road lessons at 16.