The law ain't so straightforward. There are speedlimits and very strict conditions to what is a "closed area". Your own backyard doesn't count as one if it's not fenced and secured for no one to enter the area.
There are "icetracks" where you can drive underaged but those too are pretty much history nowadays.
The traffic law doesn't count in private or closed areas but it's the enforcement of the laws that count. By the law the area would have to be both private and isolated (isolated meaning no possible accidental access from outside) which very seldom is the case.
if someone is a bad driver it doesnt matter how old they are, theyll still be a bad driver. its better to start earlier and teach proper driving techniques when the person is still growing and learning than to try and teach someone whos already set in their ways.
Yeah some do, if you meant that "can" literally. The driving license we can get when we are 18 years old or older. I have many friends who have driven car (on the fields) or kart since little kid (as soon as their feet reached the pedals).