It is a very difficult question to answer definitively.
wigwam highlighted his aunt who discussed her reduced capabilities with him while continuing to drive, before she decided to stop. How would wigwam feel if his aunt had killed someone during this time. He is caught between stopping her driving, and therefore limiting her mobility and agreeing she should continue to drive with reduced capabilities. This is a situation I would not want to be confronted with. Luckily we have only one family member in their eighties who is still driving and he is as “bright as a button”, as my granny used to say.