I raised boys and they get into all kinds of mischief.
...Especially if it is motorized. I say 16 years when they can take drivers ED and learn to be responsible.Lol prior to that...Depends on the motorized toy (like cars) and how fast they can go. It is all about safety. You as a parent should be able to run and catch them if there is a problem.The child should not easily fall out/off.