The traditional Chinese way of reckoning a person's age is completely different from the Western one. In the West, we are born at age '0', and we age 1 year at our birthday. In Imperial China, newborn start at 1 year-old, and they add 1 year on the first day of the Chinese New Year.
Hence a baby born on the 30th day of the 12th month is already 1-year old at birth. He or she ages 1 year on the first day of the Chinese New Year, i.e., the 2nd day of his or her life. So when the baby is two days old, his or her age is actually "2 years"!
As a consequence, there will always be a 1- or even 2-year difference between the Chinese age and the Western age of your characters, the former being the larger one. GMs may or may not want to take this into account for the rules about character generation etc.