Ponyboy's description of Sodapop as a colt is significant for several reasons. The first is physical. Sodapop is lean and wiry, like a colt would be. Such physicality quickly pivots to an emotional aspect. In chapter 7, Sodapop is intrigued with the media attention. He shows this through vigor and a sense of excitement. Like a colt, he wants to know what is happening and desires to be the center of attention. This description underscores his characterization. Throughout the narrative, Sodapop is true to his name as "bubbly." He is "always happy-go-lucky and grinning." Sodapop is also described as one who "gets drunk on just plain living." These reflect a person who is more entranced with the moment. Sodapop wishes to be immersed in the direct action of life, of being in the world. Sodapop is not someone who is overcome with melancholy, or resigns himself to distant reflection. He is of the moment. Like a colt, he wants to be involved with everything and wants to be immersed with the instant.
Sodapop being a colt is a reflection of his active nature. He is engaged, locked into this instant. He desires to be a part of it. Ponyboy's description of him holds significance because it is almost an exact opposite description of Darry and Ponyboy. Sodapop is so intrigued with everything around him, as a young colt would be. Darry has come to see the bitterness that life can offer and thus is a bit more distrustful, while Ponyboy is reflective of the nature of being in the world. Both of these contrast with the young, excitable, and "coltish" nature that Sodapop displays. Ponyboy's description is reflective of this condition of being in the world.