I’m Korean, but I was born in the US so it’s never really affected me much, but it was always funny trying to explain it. It gets even weirder. Not only are we 1 on the day of birth, we turn 2 on the next New Years Day. My birthday is in December so I was 2 around 2 weeks after I was born. It shouldn’t be too much of an issue in Korea because on government documents and laws they use actual age like the rest of the world. It’s only really celebrating things that the extra age is used. There’s a lot of cultural/traditional things to celebrate. The 100 day mark, as this was a common time that infants died so making it to 100 meant you were probably going to survive. Also Lunar New Year celebrations. But as far as functional things, normal age has been used, but this should limit a lot of the confusion.