The connotative meaning of the older boys making room for Jerry is so positive because it means that they are accepting him.  Despite the fact that he is younger than they, that he is a foreigner, and that he doesn't speak their language, they allow him to hang out with them (for a while at least), and their acceptance is -- to Jerry -- the most wonderful possible thing that could have happened in that moment.  To be allowed to dive and swim and splash with these older boys that seemed "like men to Jerry," gives him a sense of belonging at the wild bay rather than the "safe beach" where his mother and all the other vacationers splash and paddle.  When the boys make room for him, it makes him feel like he is grown up, too, because they are older.  He feels more independent of his mother and more adult as a result of their acceptance.