What do you think Johnny meant when he told Pony to '"stay gold"?

Johnny encourages Ponyboy not to waste his youth looking for things he doesn’t have. Johnny gets philosophical about life using Frost's poem as a metaphor. He tells Pony that life is fleeting and nothing is permanent hence "Nothing Gold can Stay". Johnny encourages Pony to see the goodness in people like Darry instead of wasting their relationship.