Probably, what the doc did to estimate his age was to measure and weigh him and compare it to other kids via the growth charts. These charts, for infants, toddlers, and children, at least, can give you an approximate age based on height and weight. But since they're based on averages, whether or not his 'official' birth date is anywhere close to his actual is anybody's guess. If the baby is 'big' or 'small' at birth, it kind of throws off the system.
“Rules only make sense if they are both kept and broken. Breaking the rule is one way of observing it.”
--Thomas Moore
"Keep an open mind, I always say. Drives sensible people mad, I know, but what did we ever get from sensible people? Not poetry or art or music, that's for sure."
--Charles de Lint, Someplace to Be Flying
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