After my Gran died my Granpa remarried to Ivy. Ivy never took a driving test because she had learned to drive many years ago. Her learning was from driving army lorries in the war. Almost fifty years later, having never driven since the war, she decided to get a car. She rarely ventured out of the village and always planned her trips well. She never ever turned right, only left. These trips took quite a bit of thinking about really.
Never crashed has far as I recall, she only went slowly and people had fair chance to get out of the way.
Now many will say "shouldn't be on the road" etc, but Ivy had to take over and run the small family farm when her father died when she was 16. She had to work the land, ploughing with a horse, earning enough to feed the rest of her family. Then the war came along and she had to help out there. Husband had a stroke and she nursed him for years, etc.etc.
I expect many of the doddery old biddies you see out there have similar tales to tell. If they want to drive, let them, they earned it IMHO. If they are not very good at it, just give them a bit more time and a bit more room, they'll be OK. And if they're not, at the end of the day it is just a car, insured and doesn't really matter on the grand scale of things.