Answer: Johnny wants his friend Ponyboy to remain forever young in mind and spirit.
Step-by-step explanation:
The Outsiders (1967) is S.E. Hinton's novel about the orphan boys - Ponyboy and his two brothers, Soda and Darry, and their teen gang called 'the Greasers'. In the gang, there are four other boys: Johnny Cade, Dallas Winston, Keith Matthews, and Steve Randle.
At the end of the novel, Johnny tells Ponyboy to "stay gold." This is a phrase from "Nothing Gold Can Stay", a Robert Frost poem which Ponyboy recited in the old church. The theme of the poem, which is also present in the book itself, is that life is short, and one should spend their youth in a best possible way. What Johnny is trying to point out is that Pony should stay forever young, kind and innocent.