Picture this: You're watching an interview with your favorite Korean celeb. The host asks for their age and you pause because they just said they were a year older than you thought. You know almost ~everything~ about them, how did you get their age wrong?
This is because Koreans follow a slightly different age system. In Western cultures, and in ours, babies are considered "zero" at birth. In the Korean age system, however, a baby is considered one year old on the day they're born—and another year older on new year's day.
Now how does this work?
There's a lot of confusion and theories as to why Koreans count their age this way: Some say they include the time you were in your mother's womb (nine months rounded up to twelve to make a year) or that calculating the Korean age came from an old Asian numerical system that had no concept of zero.
And for the extra year that they add with each new year, Koreans have used Chinese characters (Hangul was created by King Sejong, the fourth king of the Joseon dynasty which lasted from 1392 to 1910) and have adapted a lot of their culture into their own. This means that back in the day, Koreans put their age in the Chinese 60-year calendar. But because there was no *regular* calendar to follow, Koreans ignored the day they were born and just added another year on the first day of the lunar calendar.
Let's say, for example, Lee Min Ho's birthday is on June 22, 1987. In the age system we follow, this means he's turning 33 years old in 2020. But in Korea, he's actually turning 34!
Here's a video explainer by BuzzFeed:
Simple enough, right?