I'm not sure there is an age at which we all become suspect behind the wheel. But I know my father-in-law's deriving became much less trustworthy in old age. He still drove the two hours to our place from his and as far as I know never had any accident or other difficulty. But once I rode with him when he was in his low eighties when he came to attend a performance of the boys choir my stepson was in. He seemed unable to judge when it was safe to merge onto the highway and when he finally decided to go it was lucky that we didn't get hit.
Living in the country helped. But then he lost his license when he rolled his car in Point Reyes Station one night. The road at that place had a very deep, poorly marked gutter and his night vision wasn't so good. To his credit he studied the manual, passed the test and got his license back. Later, when he was in assisted living he often asked where his car was but we kept it parked at his house far from that small town where his assisted living was located.
I definitely think we need to be careful and accept that driving may not be forever. We lose everything in the end and somethings along the way.