Most people are losing their facilities years before any formal diagnosis and plenty of people, especially those who don't want to lose their freedom simply won't go to the doctor for a diagnosis. Nobody can force someone to see a doctor.
Luckily he did not put up a fight when we took his keys but up to that point he was driving a giant truck around every day, seemingly mostly on instinct. I am still thankful that did not end in tragedy before we were able to move him into a controlled environment.