For my parents it was 65-70 when I noticed and started to become very concerned for their ability to drive safety. At 75 now, my dad at least only drives during broad daylight but even so he can't maintain a safe speed and does barely half the speed limit, then complains about tailgaters not liking his "retired lifestyle" (which is his personal excuse for driving slowly, when in reality he lacks the skill to keep up with traffic, which is very dangerous in my view...)

It's a danger for sure, I think for many the best they can do is limiting their driving as much as possible to 'safe' roads. With elderly driving slowly it's more a problem of ruining their car when they crash than endangering lives. Wish there was a better solution for all of them.

Maybe less of an issue if they’re given taxi vouchers to the value of about the typical amount of driving they would have done?

Across the western world, elderly benefits increasingly outstrip the growth young workers paying taxes for their benefits are able to eke out. I do not think they need free taxis as well.

For UK in particular look up triple lock pension.

London also has the highest number of non-citizens staying in four star hotels on the tax payers dime.

I think the elderly former tax payers can have all the taxi vouchers they can reasonably use.

They just need to mutter “asylum seeker” occasionally.

There's not many taxis in most places, I come from a town of 400 people it'd be a very uneconomical solution.

I'm not saying it's great for them to drive, I just doubt there's a way to fix it in these sort of places. My grandma cycles to the small store for most of her groceries everyday, it's only the big store she drives to bi-weekly. Honestly the cycling is probably more dangerous, and there's some elderly in my town who're pushing 100 cycling daily.

Public services don't need to be 'economical'