The real issue is how to deal (or not in this case) with deteriorating capability with age (in this profession or any other). Not many companies (bus or otherwise) are really set up to objectively deal with this problem, and this case serves as a wake up call. Arbitrary bans based on age rather than capability are not fair, esp. in this age of age discrimination rules.
While I agree wholeheartedly with the first part, I can't agree with you on your last sentence. Bans based on age may be considered unfair e.g. now I'm past 70 I shall never be able to serve on a jury, which I regret, but I don't dispute the reasoning behind it. The airline pilot who managed to land his plane on the Hudson River in N.Y. was only a year or eighteen months away from compulsory retirement, which might be considered rough treatment in his case, but you have to take the rough with the smooth. I love cricket, but every summer cases arise where (sometimes great) players have played on too long and their reactions/ eyesight in the case of batsmen, or speed in the case of fast bowlers, have been found out. The retirement often comes not far into the season to save everyone embarrassment. Their shortcomings don't have any repercussions on the general public, but waiting for a bus driver to start exhibiting signs of impairment, physical or mental, before preventing them from driving is madness, possibly lethal madness at that. Bus drivers these days don't just climb into a cab and set off, knowing they have a conductor to deal with passengers, fares, queries, unpleasantness, timekeeping, etc. There has to be a cutoff - I suggest 75 absolute maximum. If I'm being illiberal, I'd agree: there's no room for liberality here. The parents of the 7 year old boy killed in the front seat upstairs just enjoying the ride, as many of us remember doing and, perhaps, still do, have been gracious in their expressing the wish that lessons be learned so that the mistakes that led to this tragedy aren't repeated. As the younger brother of a beloved boy of much the same age who also died in stupidly unnecessary circumstances, decades ago now but it never leaves you, I would endorse that.