How old is too old

On the way back from the gym I stopped for an elderly lady that is crossing, no creeping across the parking lot. She is hunched over at about a 45 degree angle, with a cane, and each stride is no more than 6 inches. I patiently wait and while I am waiting I look around to see who drove her there. NO ONE. This lady drives. Talk about slow reaction times, it really is unbelievable some of the elderly I see behind the wheel down here. I can understand they don’t want to give up their mobility but you have to draw the line somewhere. When you can measure their reaction time with a sundial it is time to give up the license.