I lived in Florida for a long time and the elderly drivers in our midst were always a major concern. And although the elderly drivers were great fodder for plenty of jokes; "Gramps puts his left turn signal on when he leaves the house in the morning and then just leaves it on all day." It really wasn't funny if you were the one driving down there everyday.
Surely you will remember that hilarious fast food commercial that featured a little old lady who could not even be seen behind the wheel of the car she's driving because she's so short. Well that's not an exageration or even an uncommon sight among Florida's elderly drivers and if you can't see them - can they see you?
I believe the tag line to that commercial was "Punch it Margaret" which brings me to another safety issue with the elderly - their depth perception becomes so diminished that they are unable to correctly judge the distance between oncoming cars and their own vehicle. In Florida I'd often have to stand on my brakes to avoid hitting an elderly person who had just pulled into on-coming traffic with all of the speed of a tortoise!
I feel that we have an obligation as their family, friends and neighbors to rescue the elderly drivers from themselves. Especially when you see these kinds of driving errors - please don't hesitate to take steps. Don't wait for a serious accident to have this conversation because the grandmother you save may be your own!! Frank talk saves lives.