Phoebe, the Carousel, and the Gold Ring:
As far as we can tell, there's only one place in the entire novel where Holden declares himself to be really happy. So happy, in fact, that he's "damn near bawling." And that moment is at the end of his narrative, in Chapter Twenty-Five, as he's out in the rain watching Phoebe go around and around on the carousel. She just looks so nice, he says, in her blue coat, going around and around. But there's more to this sunny jubilance than a kid on a carousel. A few things have just happened: 1) Holden decided that, after all, he's not going to run away, 2) Phoebe put his hunting hat back on his head, which we've already talked about as being caring and kind, and 3) just maybe, Holden has realizes that growing up isn't the worst thing in the world.
Of course, number three up there is subject to debate. We're mostly talking about Phoebe's grabbing for the gold ring, and Holden's thought that "the thing with kids is, if they want to grab for the gold ring, you have to let them do it, and not say anything. If they fall off, they fall off, but it's bad if you say anything to them."
The gold ring is something we don't have anymore on carousels. The gig was that you were supposed to reach for the gold ring when you passed it on your horse. Usually, if you grabbed it, you got a free ride. When Holden concludes that you have to just let a kid reach, even though they might get hurt doing so, he might be saying admitting (although he probably doesn't realize it himself) that growing up is in fact necessary – for Phoebe and for himself; you can't really protect a kid from it, so it's better to just accept it as it is. Or he could just be talking about a gold ring.