Among the famous writers that I know through their writings, I'd expect Jorge Luis Borges and Umberto Eco to have read many thousands of books, because that wide culture was a major element of their fictions. The later did have 50,000 books at home, but the former became blind and probably didn't own many books.
With simple math, reading 2 books each week leads to at most 7,000 over a lifetime. If Denny McCarthy's guess is right (read 85% of 20k), his older brother read about 4 to 5 books a week, every week, from teenager to his old age.
Funny that you bring up Borges and Eco. Eco when commenting on his library, I can't remember if in an essay or lecture, referred to it as an 'anti-library', pointing out that one of the most important skills a reader can possess is to be able to talk about books one hasn't read. As in Borges Library of Babel most people will be doomed to only read very little of what is in existence.
He thought his huge library should be taken as a research tool and sign of 'conscious ignorance' of the vast things you don't know, rather than taking a consumer mindset to it, which you see a lot of people do when they brag about how many books they've read.
With simple math, reading 2 books each week leads to at most 7,000 over a lifetime. If Denny McCarthy's guess is right (read 85% of 20k), his older brother read about 4 to 5 books a week, every week, from teenager to his old age.