S.E. Hinton was 16 years old when she wrote it. If you read the novel as an adult, you can easily see how the characters are a kind of school girl fantasy. It has "tuff" good looking bad boys who are so sensitive that they cite poetry, gaze dreamily on sunsets and read "Gone With the Wind" to each other.
But that is not a critique of Hinton. She is a good writer who expresses her 16 year old understanding of the world better than a lot of seasoned writers. In that sense the "Outsiders" is one of the most authentic teen novels ever written. A book written by a teen for teens.