Python "why" questions

[CM]

> Apparently, the Japanese used to (before they started adopting western
> conventions). I.e. ages were given as "in his tenth year" (meaning nine
> years old).

Koreans still do this.  The day a child is born it is "one".  Even
odder to me, the next birthday is not on the next anniversary of the
birth, but on the following New Year's Day.  So a kid who is born on
Dec 26th, will be "two" as of New Year's Day the week following his/
her birth.  (They also are aware of the "western" version of their
ages if needed).
.