Age reckoning originated in China, where it’s believed that a baby’s age starts from its time in the mother’s womb. The practice is also common in Korea, Japan, Taiwan, Hong Kong and Vietnam.
“One; it was supposed to have a positive effect on Japanese people because they would be one year younger.
Two; it eliminated the disadvantages of being born right at the end of the year which meant you turned two years old at the beginning of the following year. For example, this could impact your marriage prospects if you were a woman.
Three; it was felt that the Japanese age system needed to be brought into line with standard international practice.”
