He presumably remembers how to drive a car. Private pilots don't have to resit their flying tests annually beyond a certain age, but they do have to prove they're medically fit to fly. If you're allowed to fly a light aircraft after passing a regular medical examination which checks things like eyesight, chronic illnesses which would affect their ability to drive, and reaction times, a similar arrangement should be adequate for driving a car.

The oldies go slowly and tend to end up with some low speed impacts giving dented cars rather than injury. Maybe if you get 2 or 3 of those in a year it's time to stop.