It does sound like the OP's neighbor's accident may have just been that-an accident. Reminds me to be more careful getting on and off the tractor. But since other's have referred to older citizen's driving skills (or lack thereof), let me relate my recent experience.
Yesterday I renewed my driver's license, and what I saw was downright scary. Two elderly ladies ahead of me particularly stood out-one obviously had vision problems, and couldn't pass the vision test. But the other was even worse in my mind-this lady had to use a walker and could barely move, had trouble following directions from the examiner, had very obvious slow reaction and physical skills, yet passed the vision test so got her license renewed.
We had to take my Mother's car keys last winter, and while she didn't like it, she is slowly adjusting. My MIL is several years older, yet has very goods driving skills. So it really just depends on the individual.
Based on what I saw yesterday, I'd support a proficiency test for renewing your driver's license, at least after age 65. Butthat would probably just mean more old guys on the road with tractors!