In either the traditional or modern age system, the word ''sui'' , meaning "years of age", is used for age counting. The traditional age system is referred to as ''xusui'' , and the modern age system is referred to as ''zhousui'' or ''shisui'' .
In the traditional age system, a year is added because of the gestation time in the womb.
Japanese uses the word ''sai'' as a for both the traditional and modern age system.
The traditional system of age reckoning, or ''kazoedoshi'' , was rendered obsolete by law in 1902 when Japan officially adopted the western system, ''man nenrei'' . However, the traditional system was still commonly used, so in 1950 another law was established to encourage people to use the western system.
Today the traditional system is mainly used by the elderly. Elsewhere its use is limited to traditional ceremonies, divinations, and obituaries.
Koreans generally refer to their age in units called ''sal'' , using Korean numerals in ordinal form. Thus, a person is one ''sal'' during the first calendar year of life, and ten ''sal'' during the tenth calendar year.
The 100th day anniversary and the first anniversary of birth , call for large celebrations, and Koreans celebrate their birthdays, even though every Korean gains one year on New Year's Day. Because the first year comes at birth and the second on New Year's Day, a child born, for example, on December 29 will reach two years of age on January 1, when they are only three days old in western reckoning.
In modern Korea, the Western age system is widely known and referred to as ''man na'i'' , although the traditional system is most often used. For example, ''man yeol sal'' means "full ten years", or "ten years old" in English. The Korean word ''dol'' means years elapsed, identical to the English "years old," but is only used to refer to the first few birthdays. ''Cheot-dol'' or simply ''dol'' refers to the first Western-equivalent birthday, ''du-dol'' refers to the second, and so on.
In some countries, some people use the Western system and some use the East Asian system. Most Koreans, especially of the generation before the 1960s, consider themselves to be one ''sal'' older on New Year’s Day by the Gregorian calendar and celebrate their birthday by the instead of the Gregorian calendar. The birthday by the lunar calendar is called ‘?? ??’ and ‘?? ??’ is the birthday by Gregorian calendar.
For official government uses, documents, and legal procedures, the western age system is always used. Regulations regarding age limits on alcohol and tobacco use, as well as the age of consent, are all based on the western system .