Well, you could say that about disabled drivers but it depends on the disability. There's a guy who lives near me who has no legs (he's always arsing about) and he's perfectly capable of driving as his vehicle has been adapted to suit his needs.
All I'm saying is that Doris and Fred could be a danger to other road users. Its unlikely they will be able to react in time if they need to perform an evasive manouver.
But then you could say that about anyone, it only takes a minor lapse in concentration and you've stuffed your car.