I don't think it is a function of the age (other than limiting his available time left for work) but that he is laser-focussed on his actual work in finishing h

I don't think it is a function of the age (other than limiting his available time left for work) but that he is laser-focussed on his actual work in finishing his books. Probably necessary to achieve what he did, but somewhat frightening too. Or to envy, depending how you look onto it :)