Why should he have retired? I hear that a lot about both managers and players. But if you love the manager job or if you love to play football... why retire?
I've always felt the "should quit at the top" thing is silly. As long as something is fun you should do it as long as you can even if you are "past your peak".
Just my view ... if he's "having fun" then carry on. Personally I would come up with far better ways of having fun after 40 years at or near the top