I can empathize with your predicament Michael. My mother has M.S and is 73 yo. She decided to quit driving a year ago, after a very risky near miss which shook her confidence up severely, and after her M.S. started affecting her legs' coordination with the vehicle pedals. She's learning to enjoy getting chauffeured these days :)

Here in Oz Down Under, drivers from the age of 75 must complete annual medical assessments to retain a licence. When you reach 85, in addition to the annual medical examination, you have to pass a practical driving test every second year to keep your unrestricted drivers licence.