Unfortunately these types of incidents all have a similar theme.  It is a fact that as we age our reaction time get slower, our coordination lessens and our vision and spacial awareness decline.   I saw this first hand with my parents.  The ability to drive also means freedom and independence which is why the elderly are reluctant to give up their licenses.
How quickly the decline occurs and at what age varies greatly from individual to individual.  So the only way to evaluate this is an objective test of their driving skills.  Driving simulators are available to conduct tests like these in a safe environment.  Perhaps a requirement to be evaluated in this way for license renewal would be a way to lessen these incidents.