Don't know about chinese, but in (traditional) Korean culture, a new-born baby is already a year old. Yes, it's not 100% scientific but I guess Korean culture has been quite pro-life. We consider fetus as a living person and we count his/her age. and therefore consider a new-born already a year old. thereafter, counting is a little vague these days. In the traditional culture, people count up their age on new years day. So when a new year comes, we still say that we are a year older. but in modern culture, people count up on their birthday. traditional counting still exist today, and typically korean age = western age + 1. However, the age difference between korean and western can be two or even three sometime. That's probably because people mix up two counting methods. (a year old baby and time when counting up) So, to be exact we exchange the year we were born or our zodiac instead of the age in number. fyi, after birth, Koreans celebrate on baby's first 100th day. (because he/she survived 100 days after birth; in yesterdays, not many babies managed to survive) And surely, the first birthday. - we do think birthdays special, too.