How old? If you like books that are more than a century or so old, then don't worry, those books were made with high-quality paper that really does last. It's

How old? If you like books that are more than a century or so old, then don't worry, those books were made with high-quality paper that really does last. It's the books in the 20th century that won't. (Some might, higher-quality ones say "printed on acid-free paper", so theoretically those will age as well as books made in the 1800s.)