Some cultures celebrate an individual's coming of age into adulthood with ritual, with solitude, with thoughtfulness, or with a big party. In Japan, the annual Seijin-no-Hi holiday takes place the second Monday in January. This year that's Monday, Jan. 9, and it's held in honor of anyone who turned 20 between April 2 of the previous year and April 1 of the current one. Why such a specific range of dates? Unlike some countries, which dole out varying rights and responsibilities of adulthood to people when they turn 16, 18 or 21 years old, for instance, Japan confers the majority of its legal adulthood to people when they wrap up their second decade. Voting, drinking, smoking and other activities open up to those who are 20. The official age of adulthood has varied over the centuries, but was set at 20 in 1876. Last year estimates placed more than 1.5 million 20-year-olds taking part in the festivities.