Two examples.
1/ a while back, I drove past a stooping, elderly gentleman, who lives near my boss, working his way, using the car for support, round to the drivers seat, and opening the door. I carried on past, stopped at my bosses house, posted something through the letter box, reversed out, turned round and drove back down the road. He still hadn't made it fully into the drivers seat!! In 5 minutes +!!
2/ stopped at my local Coop. A small car had been reversed up to the kerb, on double yellows, and parked at a 45 degree angle to the kerb with one back tyre actually on the pavement. An elderly lady struggled out, hobbled to the drivers door and helped the driver out of the car. The driver was even more elderly, and needed a walker to get about!! I later followed the same car up the hill out of the village at 16mph!
Our village is full of incredibly decrepit old people, who drive incredibly slowly, nose to windscreen, and can barely walk.
Now stats might say that this group of drivers don't have accidents, bu maybe their saving grace is that they don't drive faster than 20mph, and that they tend to stick to visiting the local store, rather than epic motorway journeys. BUT, that is hardly the point. You can't tell me that someone who needs a walking frame to get about, or who takes 5 Jeffing minutes to lower themselves into the driving seat, can possibly have the reactions needed to perform an emergency stop in the event of an accident? And accidents can occur anywhere, at any time. What if a small child ran into the road, whilst they were driving through the village?
The elderly, and many other types of driver, need to be retested regularly. I know the elderly are often fiercely attached to their independence, but there has to be a cut off point!