At age 5, Sagan began frequenting the New York Public Library to browse books that could give him a better understanding of the stars. -- Mashable, 8/9/12
Props to Mashable for mentioning that Carl Sagan was a library user in its August 9, 2012, post See Carl Sagan’s Childhood Vision of Space Exploration. See Sagan's reading list.
Who Was Carl Sagan?