Age begins at one
Korea is one of the few countries that counts a newborn as being age 1 from birth. The tradition originates from China and was widely used in Asia.
From birth, a Korean starts as a 1-year-old and grows older by a year each year as the calendar changes. A 20-year-old, therefore would be 21 years old in Korean age, even if they have had a birthday that year. It's also the reason a newborn baby who came into the world just two short months ago could already be recognized as 2 years old.
Korea's civil law has been counting age based on one's birthdate since 1962. But Korean age is still widely used socially as the preceding measure in comparing each other's ages. Age remains one of key factors defining hierarchy and relations both personally and professionally in Korea.
Some say the Korean age calculation dates to agrarian society where seasonal changes and the length of a year were prioritized. Some also say it is based on an idea that the nine months spent inside a mother's womb is counted.
But as confusion persists in mixing and using two versions of one's age, most other East Asian countries have decided to abolish the dated aging system. Japan, for instance, enacted relevant laws in 1902 to officially use the universal age count, as did China in the late 1970s. North Korea is also said to be using age based on the date of birth.