Because Confucianism is a part of the backbone of Korean society, age can often dictate the nature of people's relationships.
.Age is so important for a Korean that it's one of the first things they ask someone when meeting for the first time. They will also be quick to let the recipient know their age. People new to Korea often find it odd and wonder why Koreans are so immediately interested in their age. However, it's just the way things work in Korea and there's no need to be offended. One important reason why Koreans will immediately ask someone's age during introduction is because they don't usually refer to others by their names but by age related titles. For example, a female High school student would refer to a female University student as "Ohn-nee" - meaning older sister. The equivalent for a male High school student to a male University student would "Hyong" - older brother. It's kinda like showing respect to those who are older (and wiser?!). The only exception to this rule is between two friends who are the same age. In this situation, it's commonplace to refer to each other by name.
As a foreigner living in Korea, before expressing your age, you need to learn how to calculate it. Koreans have two different age systems -
1. Birthday Age [만 나이]
2. Korean Age [나이]
The Korean Age (나이) is the more common of the two systems used.
If this is still confusing, here's an easy way to calculate your Korean age - subtract the year you were born by the current year and add one.
몇 살 이세요? : How old are you?
저는 20살 입니다. : I'm 20 years old.
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