I had a nasty situation a quite few years ago sitting in a car with my mom while my grandmother was driving. At some stage, she was coming out of a small side road and wanting to turn left onto a dual carriage way (on english roads, she'd be trying to turn right) and noticed just as she drove onto the road that she couldn't do that because being a dual carriage way there was a barrier in between. We were confronted with cars rushing straight at us from the left and in the last moment she went into reverse and drove back into the side road. Both me and my mom were absolutely shocked, started shouting at her and her only reaction was "yeah, whatever... no big deal, we're alright" but as a matter of fact we were very close to having a nasty accident. My dad on the other hand who is now 70, is an amazingly good driver. Never had an accident in his life apart from when he was doing rallys in Scotland almost half a century ago. He just has bloody good judgment of what is going on around him and predicts dangerous things that might occur on the road. So old doesn't always mean no good. None the less, I think old drivers should be tested for how well they observe the road and how good their reactions and control of the car are. If they're no good at it, just lock their gear box so they only have 1st and 2nd and take out half the spark plugs.