Yes, retest. And I like the suggestion of @lightlyseared that maybe everyone should be tested every certain number of years. But certainly we need to do something when people begin getting older. Of course, aging is very individual, and it depends on good eyes and reflexes and judgment. I know some people who shouldn’t be on the road at any age—but that’s another story.
My concern about the elderly driving is that you don’t want an accident to be the way they stop—I’m worried not so much about them hurting themselves as them hurting someone else, perhaps on a bike, or at an intersection. So, people have to stop driving while they are still doing pretty well—not when they are really doing very poorly. And somehow we need to figure out how to do this fairly.
I remember one time there was a very old man who couldn’t read the signs at the test, and the people giving the test just coached him—pretty much gave him the answers. It was ridiculous—and he was renewing his license for 5 years. He couldn’t have been less than ninety.