I will use stereotypes here for the sake of convenience.
A husband, whose wife does not do paid work, retires. They no longer need two cars so they sell her car. He takes over the day to day driving and they rarely go anywhere alone. She starts to lose her driving skills and road confidence. There comes a day when she just no longer drives at all. Her husband has a stroke and along with the stress of dealing with illness, she has the added stress of having to drive, not having done so for years.
Usually among couples, one or the other is the usual driver, rarely sharing equally. I would suggest that allowing the non usual driver to drive at least one quarter of the time is a good idea to keep their driving skills intact for as long as possible.
Can't you see I am getting old when I start thinking about things like this!