All I would say is that we are not allowed to drive until we reach 17 and pass a test, what is the difference on setting an age when we need a review by a third party, as to whether we need a retest or to stop driving. Diminishing ability mostly is a gradual process and many will not see the problem. I Know of one old lady who has had her license revoked but insists that it has only been sent to the DVLA to be “updated” she still drives. I have no problems in reporting her if I see her driving.