Cico, Samuel, Florence, and Jasón
These four guys get lumped together, because each in his own way shows Antonio that there might be something more out there for Antonio than Catholicism. Jasón has his Indian friend, Florence doesn't believe in God because of the horrible things that have happened to him in his life, Samuel introduces Antonio to the story of the golden carp, and Cico actually shows Antonio the golden carp. And Cico lays out Antonio's inner struggle more directly than anyone when he says, "'You have to choose, Antonio […] you have to choose between the god of the church, or the beauty that is here and now'" (21.41-43).
The death of Florence marks the beginning of the end for Antonio's journey. Once Florence dies, Antonio's faith is shaken to the core. Florence's death stands as the event that will lead to Antonio's final transformation from boy to man because it's Florence's death that makes Antonio eager to leave for his uncle's place in the summer, and that separation from his parents and immediate family force him to do a bit of growing up on his own.
As Antonio prepares to leave for the trip to get away from the memories of Florence, Ultima says to him, "Be prepared to see things changed when you return" (22.86). And indeed they change—a lot. When Antonio returns from working with his uncles, he has to handle final showdown with Tenorio and the death of Ultima. By now it's clear that Antonio simply is not the boy he was at the beginning of the novel.
Guys like Horse, Bones, Abel, and the Vitamin Kid spend their days horsing around, racing, spitting, peeing, fighting, swimming, and engaging in what most would call normal childhood behavior. While he has his conflicts with the gang throughout the book, Antonio finds comfort in them. When he's with them, he can hold onto his youth and avoid the loss of innocence that comes with growing into a man.