There comes a time when people need to stop driving, both for their own sake as well as for general public safety. The data says that once one gets into one's 70s, the fatal wreck probability curve starts going up pretty steeply with age. By age 90, death behind the wheel is pretty likely for those who persist.

Everyone should have a trusted young friend or relative to tell them when "it's time". By the time one is in one's fifties, it should be obvious that one's reflexes, both physical and mental, as well as one's vision and hearing, are not what they used to be. It is then time to start planning for the day, not far away, when one will surrender one's license, hopefully with grace rather than after someone reports you and you fail the miserably easy retest or simply die in a wreck.