We can apply the word classic to literature and other art that is a model of its form. Classics are works that have been widely seen or read, and often imitated, but never surpassed. True classics, however old they may be, never grow stale.
Most "classics" are at least 95 years old, and most authors of classics have been dead for at least 70 years, but sometimes we press the word into use to praise newly-created works.
Most classic books are in the public domain due to their age (except those few books for which a government has granted a perpetual copyright), and are freely available online from Project Gutenberg at http://promo.net/pg