barry: right on! i'm only 39, but due to changes in my health (RSDS, a form of neuropathy or nerve damage), i've already noticed corresponding changes in my ability to drive. used to be, driving a cruiser from midnight-0800, my night vision was excellent. not so anymore, and as a result i voluntarily don't drive after the sun goes down.
same with my feet getting numb and/or the electric-feeling "jolts" in my legs. i'm not going to drive on a day when i can't even feel the pedals or i have waves of jolts that might cause me to suddenly nail the excelerator and cause a crash.
thing is, i'm also hyper aware of health/driving issues; my mom at age 69 and LEGALLY BLIND was reissued her driver's license. the very next day she was driving and killed a pedestrian. she wasn't charged; witnesses said the man walked out in front of her. even so, who knows -- with faster reflexes and better vision, my mom might have been able to avoid hitting him; he might be alive today.
even with that happening, the lic. bureau STILL LET HER keep her license! it came down to her feeling so guilty about it that made her surrender her license and give me all sets of her keys.
bottom line: if we can't depend on individuals to "do the right thing" when the time comes, something else is going to have to happen -- or we'll end up with a lot more corpses due to accident-prone drivers.