Etiquette on giving negative feedback on a top mathematician's work
The person we're talking about has his place in mathematics cemented whatever he says or does in the latter days of his career. The mathematicians who have been asked to comment on the latest claim know this and do not feel the need to tarnish his reputation by commenting publicly on it. Those who know him well may choose to tell him in private what they think, which he may or may not accept.

At its core, this is a very private story about aging and all of its associated effects. It is magnified by the fact that the person in question is a giant in his field and the public nature that comes along with everything he says. But I'm sure all of us with aging parents/friends/loved ones can relate to the fact that there are no easy ways to deal with this; dealing with it in public does not seem the right approach to me.