I think you actually do have to show you are medically fit to drive at 70. You have an eye test, hearing test, heart etc. If you're not fit, you have to do certain things to get to the required level of fitness. My father-in-law had to do it.
I agree about worries concerning old people but by far more worrying is the number of young people who drive fast and dangerously. The number of crashes involving young people, often resulting in death, is frightening.
Because we have long, sraight roads, crossing endlessly flat land, people go at crazy speeds and often end up in the deep dykes that run beside the roads. Last weekend another two young people died this way. The car was being driven by a 14 year old.