The age of consent in Korea is 16. Is this 16 in Korean age or 16 in international age?

International age is the legal standard here. The concept of Korean age is a traditional cultural construct that has no legal standing at all. The age of consent was only recently raised due to domestic and international criticism and pressure. It had been set at 13 years old for many, many years. 

Age of majority and age of consent both use International Age.  There are some laws, such as getting into movies, which still use Korean Age, but the big ones above do not.

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See Note 2 near the bottom of the page:  https://klawguru.com/2017/08/26/the-confusing-lega...

On earth, a 365 day year (366 in a leap year) is a year. There is no country-specific definition of a year. 16 years is 16 years. There's no "international age". A year is a year.