Even at a rate of 100 person days per body, that would use up 1% of the population per day. An initial population of 100 million, killed off at this rate, would have only one person left after five years. In the novel there were many corpses around that clearly hadn’t been eaten; if only half the bodies were eaten, the population would last half as long. No way a kid lives to be seven when born into a world where the main food is cannibalism.