most over 80 know when to give the keys up, particularly when prompted by families and their doctor.
I think if you mixed with enough people in the over 80 age group you'd realise that this probably isn't true, except for being told to stop by their doctor, when they must stop. Doctors are reluctant to do this, though, a friend's father with vascular dementia was told by his doctor he could carry on. He'd never been in a car with him, of course! His daughter supported him in that and told me "he only drives to the supermarket back". Many families are complicit in keeping loved ones on the road because it's easier for them too.
I personally know of many people who refused to give up. One was almost blind with AMD, one had Parkinson's and when his wife sold the car just bought another, one had dementia and was unable to live without a carer, who he drove to the supermarket to get the shopping, one drove at crawling speed on A roads, another had dementia and drank like a fish and drove, a friend's mother with dementia crashed and killed her father, I was stationary in a half empty car park once when an elderly driver reversed into me, my own father only gave up when he caused an accident (and he hadn't reached 80)..
And that's just me. We all know them if we know older people.
There is so much bound up with driving. Independence, spontenaiety, convenience, lack of obvious cost for a single journey, helping friends who don't have a car. It's a hard, hard thing to give that up voluntarily and being nearly in that age group with many friends who are in that age group, you can see how many just can't face it.
At my last appointment with my opthalmologist told me that he had to tell a guy that he couldn't drive any more. He said the man thanked him cheerfully and told him that all he needed was to be told by someone in authority, he couldn't face taking the decision himself.
I do agree that if you look at the stats of accidents per mile driven, 70 is too young to insist on anything more than a sight test, but I think we should be hotter on cognition and physical problems from 75 when the stats show things starting to go pear shaped.