S.E. Hinton's seminal young adult novel The Outsiders contains Robert Frost's poem titled "Nothing Gold Can Stay," which proves to be an especially provocative choice. Hinton clearly chooses to incorporate this poem in order to reinforce the themes that she highlights throughout her novel. Frost's poem deals with the fleeting nature of youth and beauty. Frost opens the poem lamenting that leaves will eventually fade, that the day must eventually end, and that ultimately nothing lasts forever. This poem is particularly potent within the confines of The Outsiders. The Outsiders is a coming of age story, a bildungsroman, and documents the end of youth and innocence of a group of boys.
The poem gains additional credence when Johnny writes a note to Ponyboy encouraging him to "stay gold." Johnny does not want Ponyboy to end up fading and losing what makes him an individual.
These are just a couple of interpretations that you can use to approach the topic. Good luck to you!