East Asian age reckoning refers to a few different systems of counting people's age that have been used in East Asia for thousands of years. People are born at the age of "one", i.e. the first year of their lifetime, and on New Year's Day (or Chinese New Year for the Chinese) one year is added to their age.[a] That is, age is the number of calendar years in which they have lived. It uses an ordinal numeral instead of starting with "zero" years of age, which would be the cardinal age number. (However, under the cardinal age system the number is always positive, starting with one second and not measuring years until one has elapsed.) Since age is incremented at the beginning of the lunar or solar year, rather than on the anniversary of a birthday, people are one or two years older under Asian reckoning when compared to the international age system. Therefore, celebrating a birthday under East Asian age reckoning would not coincide with the incrementation of age from one numeral to the next as it would normally, so one's first birthday would be celebrated while they are in their second year.
The system originated in China and continues in limited use there along with Japan and Vietnam. It is common enough in South Korea to the extent where it may be known as "Korean age" (seneunnaior "counting age") and contrasted with "international age" (in China the term "real age" is used; in Japan, "full age"). South Koreans are also familiar with "year age", determined by the birth year and the current year. Eastern Mongolia has a different system for measuring a person's age, which is based on the number of lunar cycles that have passed since birth (for boys; girls are measured from conception).
See also: Chinese first birthday
In either the traditional or modern age system the word sui (traditional Chinese: 歲; simplified Chinese: 岁; pinyin: suì), meaning "years of age", is used for age counting. In Chinese usage, there are three different types of age reckoning systems:
Both the "traditional age" and the "modern age" have lost much of their popularity within China, and the "real age" is nowadays the most commonly used age reckoning system in China.[failed verification] Of the three, only the "real age" (shísuì) is legally used when reporting age in an official document such as the passport, ID card or a bank paper. The "real age" is also the only one legally admissible to start drinking alcohol. The "real age" is the current Chinese legal system of age reckoning.
When a child has survived one month of life (29 days, if using lunar month reckoning) a mun yuet (Chinese: 滿月; pinyin: mǎnyuè) celebration can be observed, in which duck or chicken eggs dyed red are distributed to guests to signify fertility.
Koreans who use the traditional system refer to their age in units called sal (살), using Korean numerals in ordinal form. Thus, a person is one sal ("han sal", 한살) during the first calendar year of life, and ten sal during the tenth calendar year. Sal is used for native Korean numerals, while se (세; 歲) is used for Sino-Korean. For example, seumul-daseot sal (스물다섯 살) and i-sib-o se (이십오 세; 二十五 歲) both mean 'twenty-five-year-old'. If the international system is used ("man-nai" (만나이)), then the age would be 만 스물다섯 살 (man seumul-daseot sal). South Koreans speaking of age in the colloquial context will almost without question be referring to the traditional system, unless the "man" qualifier is used.
It is a common belief among South Koreans that the East Asian age reckoning system exists to respect the person's life from the moment of conception. 
The 100th-day anniversary of a baby is called baegil (백일, 百日) which literally means "a hundred days" in Korean, and is given a special celebration, marking the survival of what was once a period of high infant mortality. The first anniversary of birth named dol (돌) is likewise celebrated, and given even greater significance. South Koreans celebrate their birthdays, even though every South Korean gains one 'sal' on New Year's Day. Because the first year comes at birth and the second on the first day of the New Year, children born, for example, on December 29 will reach two years of age on the New Year's Day, when they are only days old. Hence, everyone born on the same calendar year effectively has the same age and can easily be calculated by the formula: Age = (Current Year − Birth Year) + 1
In modern South Korea the traditional system is used alongside the international age system which is referred to as "man-nai" (만나이) in which "man" (만) means "full" or "actual", and "nai" (나이) meaning "age". 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. Cheotdol or simply dol refers to the first Western-equivalent birthday, dudol refers to the second, and so on.
The traditional system has not been used in modern North Korea since the 1980s. South Korea is now the only country that uses the East Asian age, which may consequently be referred to globally as "Korean age".
A Korean birthday celebration by the lunar calendar is called eumnyeok saeng-il (음력 생일, 陰曆生日) and yangnyeok saeng-il (양력 생일, 陽曆生日) is the birthday by the Gregorian calendar. In the past, most people used the lunar calendar (eumnyeok saeng-il) to tell their birthday rather than the Gregorian calendar (yangnyeok saeng-il), but nowadays Koreans, especially young generations, tend to use yangnyeok saeng-il for telling their birth dates.
For official government uses, documents, and legal procedures, the international system is used. Regulations regarding age limits on beginning school, as well as the age of consent, are all based on this system (man-nai). The age qualifier for tobacco and alcohol use is actually similar to, but distinct from the East Asian reckoning system. A person is allowed tobacco and alcohol if it is after January 1 of the year one's age turns to 19 (real age). This is the "year age", which is basically (Korean age – 1), or when a person's Korean age is 20.
The traditional Japanese system of age reckoning, or kazoedoshi (数え年, lit. "counted years"), which incremented one's age on New Year's Day, was rendered obsolete by law in 1902 when Japan officially adopted the modern age system, known in Japanese as man nenrei (満年齢). However, the traditional system was still commonly used, so in 1950 another law was established to encourage people to use the modern age system.
Today the traditional system is used only by the elderly and in rural areas. Elsewhere its use is limited to traditional ceremonies, divinations, and obituaries.[original research?]
Japanese uses the word sai (歳 or 才) as a counter word for both the traditional and modern age system.
Because of the idea of yakudoshi or unlucky years, kanreki is a special occurrence for celebrating 60 years of life, meaning someone has returned to the same combination of zodiacal symbols that governed the year of their birth.
Having been influenced by Chinese culture, the ancient Vietnamese also used this system and, despite not being the official age on papers and in daily usages at the present, the East Asian age is still in limited use by adults, especially old people in rural areas. However, this age system is not really familiar to the younger generation. In Vietnam, it is called "tuổi mụ" ('her age'), "tuổi ta" (literally "our age", contrasting with Western age "tuổi Tây") or "tuổi âm" (Lunar-calendar age).
In Eastern 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.
Anheuser-Busch InBev (AB InBev) owned beer brand Harbin Beer in China (where the legal drinking age is 18), decided to fill that spot on the birthday wishlist by gifting the last person to turn 18 in China, Tian Jimo, with her own personal Harbin Beer tap and a lifetime supply of beer. (...) The promotion serves as a show of sympathy for Jimo who had to watch all her friends who turned 18 over the course of year enjoy a beer while she couldn't – at least legally that is. Tian Jimo and Tian Jichu are none other than a pair of twins who made news as babies born across two millennia with the former entering the world at 23:59 hours on 31st December, 2000
Koreans are considered one year old at birth and added another year at New Year's....some Koreans may use American age counting convention while others still follow Korean convention. To eliminate this confusion, Korean asked '만나이(Man-nai)': the same as the U.S. age counting convention.
시기나 햇수를 꽉 차게 헤아림을 이르는 말.(trans. The word refers to calculating full years or periods.
I. (명사) 어린아이가 태어난 날로부터 한 해가 되는 날. (II ) 1. 생일이 돌아온 횟수를 세는 단위. 주로 두세 살의 어린아이에게 쓴다. 2. 특정한 날이 해마다 돌아올 때, 그 횟수를 세는 단위.
최근 이승엽의 아버지 이춘광씨는 보통 양력생일을 치르는 요즘의 추세와 달리 이승엽의 음력 생일(1976년 8월18일)을 치르는 사연을 밝혀 화제가 됐다 (trans. It was a recent topic that Lee Chun-gwang, the father of Lee Seung-Yeop, revealed the reason why Lee Seung-Yeop takes his lunar birthday on August 18, 1976 instead of the solar birthday as opposed to the current trend.)
한국의 경우 만 20세로 성년이 되며(민법 제4조)...연령의 계산은 민법 제155조 이하의 규정에 의하나, 출생일을 산입한다(동법 제158조). 1977년의 민법 개정으로 혼인에 의한 성년의제(成年擬制)의 제도를 도입했다..대통령선거법·국회의원선거법·국민투표법·지방자치법·지방의회의원선거법·미성년자보호법 등에서는 이 원칙이 적용되지 않는다.
"청소년" 이란 만 19세 미만인 사람을 말한다. 다만, 만 19세가 되는 해의 1월 1일을 맞이한 사람은 제외한다.