I had almost the exact same thing happen to me a couple of years ago. I was really ticked off. When I finally pulled up along side the other vehicle, I saw some very elderly guy driving the car, totally oblivious to all that was around him. It seemed pretty obvious that he wasn't even aware of cutting me off.
You have to remember, some of these folks may not be able to
see very well; they probably can't
hear very well; they probably can't control their bladder half the time; they're taking at least 8-10 various medications, and they have to think twice about where they're going, because they keep forgetting. But, they obviously think they're okay...after all, they're
still allowed to drive a car.
We need to remember that some elderly people are driving a car
right now...and they don't even realize it.

I guess I shouldn't make fun of these folks. I'll probably be in the same boat in a few years.