Everyone mentions cognitive abilities, which is also important, but really physical abilities should be tested as well.
Here in america, My 89 y.o. grandmother (at the time) used canes to get around. Got her license renewed just by a written test, no one batted an eye. The fact that she "walked" in was enough and no one saw that she would physically have to pull her leg up to push the brake pedal.
She got into quite a few fender benders after that, and 1 pretty bad accident that totalled her car. That bad accident was responsible for a huge decline in health. She cant drive any longer, but between the insurance and the burden on family to support her ailing health, it all could have been avoided if they required a doctor's signature for renewal.
I do realize that something like this takes away from feeling independent and maintaining autonomy, and i feel for that. It sucks that part of growing old is...well, growing old, but should those emotions outweigh personal and public safety?