Considering a baby born on December 31 as two years old on January 1st actually has a couple of different reasons behind it. It goes back to three different things: 1) the traditional Korean calendar is different from ours. 2) The young people are borrowing our New Year’s holiday. 3) The way they count age in the orient doesn’t start at birth.
To begin with, Koreans traditional use what is called the Lunar calendar. We use the Gregorian calendar in the west except for the Orthodox church in Romania who uses the Julian calendar. The Gregorian calendar was invented by a Catholic priest, and our old calendar was the Julian calendar. The Julian calendar was invented by Julius Caesar. The change in calendars is why there is confusion about when religious holidays should be celebrated sometimes like making two Easters or two Christmases if you are in Romania. they call one the Orthodox Easter or Christmas because it was the original date on the Julian calendar. They call the Easter or Christmas we celebrate the Catholic Easter or Christmas because a Catholic priest made our calendar. Ours is the newest. The Orientals also have an old calendar. The young people are using the Gregorian calendar for business, but the Lunar calendar is still around, and the old people prefer to use it.
On our Gregorian calendar, New Year’s day comes on January first. On the Lunar calendar, New Year’s is slightly different every year, but comes more toward the end of January to mid February. It is one of the biggest holidays of the Korean year. The Koreans haven’t traditionally celebrated birthdays the way we celebrate them, on the day we are born. The Koreans traditionally think of New Year’s Day at their birthday, everyone. The old people in Korea don’t celebrate birthdays like we do, but the young people have begun celebrating the way we do. On New Year’s day in the old custom, everyone is a year older, so if they are thinking the old way, a baby born that year would be a year old on New Year’s.
There is another reason they add another year to that baby’s birth too. In Japan, in China, in Korea, and probably in some of the other oriental countries, they begin counting age from the time of conception, and not from the time of birth. When a baby is born in the west, they are zero years old. However, in Japan, Korea, and China, they are considered a year old when they are born. They count that time the baby is in the mother’s womb as the first year of the baby’s life.
Between a baby being a year old when they are born, everyone having a birthday on New Year’s, and the young people of Korean embracing our New Year’s day, it accounts for calling that baby born on December 31st two years old on January 1st. It is the old meeting the new if you are using January 1st as New Year’s Day. However, traditionally, they wouldn’t be two years old until the middle or end of February when the New Year’s holiday comes on the Lunar Calendar.