You’re Already a Year Old!
In Korea, rather than being born at age zero and turning a year old on your first birthday, Koreans are born at one year old. That means that whatever your age is, add one, and that would be your actual age if you were born in Korea.
The reason for this is that Koreans think that since it takes about nine months to grow to maturity in the womb, it makes sense to have a baby born at one year old.