I used to read books with ease but have had to limit my reading to online texts, both short and long form, mostly technical. I know for sure that I am not a reader anymore, because whenever I pick up a book I can't sit through it. It's an entirely different mode of consuming text, for me, one that I would have to relearn.
I struggled to read books while I was working. When I retired and suddenly stopped getting hundreds of emails every day, my book reading ability--my general ability to focus--came back. I read a lot of books this year, including long novels (1Q84...much longer than it should have been) and histories.