There's really no set age that an elderly person should stop driving and it all depends on how aware the person is and if they are actually able to drive the vehicle.
I know a guy who is 100 years old and he's a great driver and I would trust him to drive more than I would trust some new drivers.
But then again there are 70 to 80 year old drivers that do not need to drive so it's not just the age it's whether or not the person has good eyesight, good memory, good reflexes etc.
A persons drivers license should not be taken away from them just because they are a certain age and as long as they can safely drive they should be able to drive.
Some people quit driving around age 70 to 80 and some people continue to drive.
But if the person is getting too dangerous to drive then the keys should be taken away even by a court order.
But only do so if the person is not really safely able to drive.