Did you know that koreans do not calculate their age in the way most of the world does .

When a child is born they consider it to be 1 year old , taking in consideration the time child spent in the womb. One year is added to the age on New Year and not the actual birthday. For example, if the current year is 2021 and the year you were born is 1992, you’ll add one year to the current year (2021 + 1) and subtract your year of birth. This is (2021 + 1) – 1992 = 30.

korean society places heavy influence on age . It determines your heirarchy and place in society and how people younger than you will address you. How you will call your friend and cousins depends on age.

Source https://www.90daykorean.com/korean-age-all-about-age-in-korea/