One needs no license to buy or operate a car on private property. There are no age or background requirements for use on private property. Licensing tests for use on public property covers only the basics of safe operation. No training is required for adults to get the license, only passing a simple test. The license is then good in all 50 states, thanks to treaties between the states.
Vehicle registration is solely for taxation purposes to pay for public roads.
If a vehicle never goes on a public road, it doesn't need to be registered or taxed. No other guns would be taxed. Very few guns are truly unsafe. They are designed to propel a projectile when appropriately manipulated. Furthermore, the fact that national patterns show little violent crime where guns are most dense implies that guns do not elicit aggression in any meaningful way.