Take your birthday and subtract it from the current year.
Right now it's 2013, and I was born in 1992.
2013 - 1992 = 21.
Now, add 1.
21 + 1 = 22.
Koreans start counting their ages when they first appear in the stomach. Babies stay a little less than a year in the womb, so that would basically be about 9-12 months more older than your Western age, however they round it which is basically a year or so. You say Koreans are older by two years, right? This is the FIRST year where you're older.
What's the SECOND year?
Every Lunar New Year, your Korean age is raised by one. In other countries, you add a year on your birthday, but in Korea you add it every Lunar New Year.
The Lunar New Year date varies. Usually it's around the end of January and the beginning of February. This year (2013), the Lunar New Year date was on February 10th. Next year (2014), it's on January 31st. Like I said before, you add your birthday year on Lunar New Year, NOT on your actual birth date.
So my Korean age would be 22.