I'm fairly sure it's bs, or he is much older (~80), and possibly disabled and that's all he does.

I read fast, and voraciously, so my "number" is pretty high, so high most think I fake it too, but I don't. I think my goodreads profile has over 1200 books and I know I've read a lot more than that (just need to find them all on GR and get the marked). Even so, I'm probably barely sitting at 2400. I'm 40 and have been reading regularly since I was 5. Back then, I'd easily go through 10 books a week (short, and between 5-15 or so, I went to the library twice a week and I think 5 out per time is the limit). As I'm older, I probably average 1.5 a week. This summer I did probably 10-12 a month, but didn't finish anything this week at all, and I go as much as a month where I don't find anything good (and then I find a bunch and read them down).

Yeah, even if I read just as much between now and 80, I'd probably barely hit this guys number and I know I don't read as much as when I was 5-15 and didn't have a job or many time consuming hobbies. If I was disabled or something, maybe. But I don't like crap books either, and I'm not sure there are quite 6000 good books in science fiction. Amazon Kindle unlimited has what seems to be about 6400 listed, but that doesn't include everything, and there are probably other many duplicates. So dunno, I guess it's possible, but he's a true outlier if otherwise bibliophiles look at me like I'm some sort of freak, or abnormal.