When do Newchildren turn One in The Giver?

All Newchildren turn One at the first December Ceremonies following their birth.  This means that some, who were born soon after the previous December Ceremonies, would already be walking when they are named and given to their assigned family unit, while others, who had been born at the end of the year just prior to the present December Ceremonies, would be infants, perhaps only a few days old.  Under this system, there could be a full year difference in actual age between the oldest and the youngest Ones; obviously, since all children progress to the next year in age together each year, this span continues until the last recognized age classification, the Twelves, and probably beyond.

Only fifty Newchildren are born each year.  From the time they are born until the time they are presented to their assigned family unit, Newchildren are cared for by Nurturers in a common Nurturing Center.  At first, each Newchild is identified by a number only, but at the time of the first Ceremonies after their birth, the Newchildren are given names selected by the Committee and posted beforehand on a list displayed at the office in the Nurturing Center (Chapter 2).