I know you're trying to make a reduction ad absurdum, but these are arguments that are actually made. For one, this is exactly the reason why we don't allow you

I know you're trying to make a reduction ad absurdum, but these are arguments that are actually made. For one, this is exactly the reason why we don't allow young people below a certain age to drive on public roads. Furthermore, if I remember correctly, at least some jurisdictions have laws on the books that old drivers can have their licenses taken away if they are not able to operate a car safely anymore. I'm not sure if any jurisdictions require old drivers to actively demonstrate their competency in an exam or such, but I have definitely seen people argue for that idea. I'm not opposed to it either, and in fact I would not age-gate it. If train drivers or airplane pilots are required to prove their competency on a regular basis, why should we not require car drivers to do the same, maybe every 5 or 10 years?