On the other hand, when his doctor flagged my 80+ year old father-in-law as a possible risk, he lost his driver's licence after failing his driver's test, mainly because he did not do proper shoulder checks when changing lanes.

We encouraged him to practice and try the test again using both the side mirrors and physically checking over his shoulder and he did and had his licence was reinstated.

Age never seemed to affect his driving ability, just an ingrained bad habit, which he managed to change and we never felt that anyone was at greater risk for him being on the road, despite his age or the fact that he also had some physicial handicaps.