1) "Sophistication," finds George and helen sharing an equally desired kiss, but the kiss brings awkwardness between them, and they go onto play with each other as children would for one last time. From the chapter's context, I believe that the :"mature" thing is a combination of lonliness and silence. Both of them have relished true companionship and blossomed in each other's company because of it. Having to grow up and face things alone makes the mature life possible not desirable.
"They feel relieved to play together one last time as children but the story ends with their symbolic acceptance of their transcendence into an adulthood in a modern world."
2) "George's departure for the big city is a time of rebirth for him as he will start fresh, in his role as a man. He is leaving the nest, so to say, so the spring time is appropriate. The metaphor continues with the phrase, "The treesare maple and the seeds are winged." George is the seed who is flying off to a new soil."