Originally Posted by DamianJ

"East Asian age reckoning is a concept and practice that originated in China and is widely used by other cultures in East Asia, which share this traditional way of counting a person's age. Newborns start at one year old, and each passing of a Lunar New Year, rather than the birthday, adds one year to the person's age. In other words, the first year of life is counted as one instead of zero, so that a person is two years old in their second year, three years old in their third, and so on.[1][2] Since age is incremented on the new year rather than on a birthday, people may be 1 or 2 years older in Asian reckoning than in the Western system.

Today this system is still commonly used by some Chinese people.[citation needed] The system is also widely used by Koreans, with the exception of the legal system and newspapers. In Eastern Outer Mongolia, age is traditionally determined based on the number of full moons since conception for girls, and the number of new moons since birth for boys. In Japan it is used for traditional fortune-telling or religion, and it is disappearing in daily life between people in the city."

http://en.wikipedia.org/wiki/East_Asian_age_reckoning