Richie had felt a mad, exhilarating kind of energy growing in the room. . . . he thought he recognized the feeling from his childhood, when he felt it everyday and had come to take it merely as a matter of course. he supposed that, if he had ever thought about that deep-running aquifer of energy as a kid (he could not recall that he ever had), he would have simply dismissed it as a fact of life, something that would always be there, like the color of his eyes . . . . well, that hadn't turned out to be true. the energy you drew on so extravagantly when you were a kid, the energy you thought would never exhaust itself—that slipped away somewhere between eighteen and twenty-four, to be replaced by something much duller . . . purpose, maybe, or goals . . . . which theme would be advanced by the tone in the above passage best?