I keep getting confused when Koreans ask my age, and I noticed people treat each other differently based on?

Korea actually changed its official age system in June 2023 to align with the international standard, so legally everyone is now counted by their actual birth date just like in most other countries. However, in daily social interactions, the traditional Korean age concept still matters a lot culturally.

In the old Korean system, you were 1 year old at birth and everyone gained a year on January 1st regardless of their actual birthday. So someone born in December would turn 2 in Korean age just a month after being born. While this is no longer the legal standard, people still use it socially because age determines how you speak to each other in Korean. The language has different levels of formality called 존댓말 (formal) and 반말 (casual), and using the wrong level with someone older can come across as disrespectful. When Koreans ask your age, they are usually trying to figure out whether to use formal or casual speech with you. People born in the same year are considered 동갑 (same age) and can use casual speech with each other right away. As a foreigner, most Koreans will be understanding if you make mistakes with speech levels, so do not stress too much about it.