Listing old, famous intellectual people that have retained their wits is poor a excuse for evidence, since we don't know the ratio between old and famous intellectuals that have lost their wits vs that have retained them.
I didn't mean to show by these examples that this is the default, or even that it's common. I don't think it is. But I hope it's getting better, mostly thanks to the technological progress which can be stimulating for those who choose to make use of it.