This reminds me of an old Dear Abby column (or was it Ann Landers?). Anyway, everyone knew Grandpa was no longer safe behind the wheel, but no one wanted to be the one to tell him it was time to give up driving. At a family gathering, Grandpa hit put the car in drive instead of reverse. Sadly, his grandson was standing in front of his car. Grandpa's mistake cost his grandson both legs.
Elderly drivers don't make up a very high percentage of the motorists I encounter on a daily basis, but they are the majority of the motorists who put me at risk by not seeing me. By the way, I ride in a class 3 flagger's jacket, so I'm not exactly invisible. We all need a trusted friend or younger relative who will tell us when "it is time".