Why to we let old people drive?

I saw on the news this morning that a Metro train hit a car. They interviewed the driver (a man in his late 60s) who said that "it's hard to see: it's gray, it blends in with the buildings...." Blends in? It's a friggin train. How do you not notice a train? One has to be profoundly stupid to have a wreck with train, and I doubt this guy is any exception.