Age is truly a number... it has to do with reaction (IMHO) and the type of driving. If someone lives in a rural setting... the risk of someone pulling out in front of them is less. Our case was different.. lots of traffic, aggressive drivers that don’t use blinkers, rush hour etc... That is why I have always thought that some older drivers drive slowly.... perhaps they drove a lot during a time of less congestion and they are trying to be careful. Reaction time lessens as we all age (or so I am told). The type of driving where we are simply takes a lot of reaction time.
Yes reaction time increases and injuries and chronic problems add to it.
It does depend. My 92 year old neighbor is fine driving, and i think he himself is aware of whatever limits he has, like I never see him driving at night. My father in law who’s 75, he’s had to stop driving.