At 73 Philip Roth is still blasting out great novels even as the Library of America enshrines him in deluxe editions. In October Roth will publish Exit Ghost, his ninth and (he says) last novel about his fictional double, the writer Nathan Zuckerman. He, like Roth, is dealing with the ravages of age. Zuckerman is also facing the waning of his artistic powers. Roth, not so much.