Grandson, 10 this summer, has just begun reading paperbacks with the smallest print. He does not like small print, but the book catches his interest he will read it. Granted, he needed glasses the first of the year, but the glasses corrected his vision better than 20/20.
I think it's a physical development thing for the child to be able to read smaller print. We got around it by searching for various publications of a book he wanted to read, as different publishers, or even printings, would be different size or type of font. We also hit the large print shelves at the library.