my father willingly stopped driving when he was 85. His last drive ended with him rear-ending someone at a stop light, and he decided it made no sense for him to continue. A couple of years later he had starting to suffer from dementia and wanted to drive again. His excuse was driving himself in an emergency. I told him that he could drive in an emergency without a license.
I have resolved to stop driving at 85. Obviously, I don't know if I will still feel the same way when I get there. Seems to me that a lot of older people spend so much on their vehicles that they could easily afford other transportation modes if they stopped those expenses. It seems like it's a lot easier to budget for a car though, we're all used to having that be a fixed expense.