If his grandpa really drives this poorly he will lose his ability to drive well before it expires either directly from accidents, from losing his license after accidents, or from his insurance becoming too expensive. I'm always amazed at how badly die-hard FSD supporters think humans drive

Where aren't they? Over here driver's licences expire.

In the U.S. they expire but you're usually not retested unless you move states and sometimes not even then. You usually just go down to the state's motor vehicle office and confirm your info is correct, pay the renewal and they print out a new license

Yep, the extent to which people are allowed to renew their license in the U.S. is very nearly criminal (both in the cases of old age and in previous history of driving impaired or recklessly). It's one of the less talked about externalities of the States being a car-based culture. Here, driving is considered a right more than a privilege, whereas in most other first world countries (e.g. most of Europe) the opposite is true.