Korean age dates back to the moment of conception. They consider time spent in the womb as time being in existence. The moment you are born you are also one year old. The formula is something like current year, minus birth year, plus one year.
I'm not Korean, so my math could be off. I only know this from dating Asian guys. It is just one of those things I wish I didn't know about actually, like "fan death" and such.
Thanks for your explain. I wanted to explain about Korean age. but ,you know, my English pretty bad.