Coming of Age Day, also known as Seijin no Hi, is celebrated on January 09, 2017. The day is a Japanese holiday, held annually on the second Monday of January. On this day everyone who has reached the age of majority, so everyone who turned 20 during the past year, received congrats. Everyone who turned 20 should realize becoming an adult and therefore celebrate the day, on which coming of age ceremonies are held. Also, a lot of people celebrate together with friends and family.
Those celebrations already existed since at least 714 AD. Back then, a young prince donned new robes in order to mark his passage into adulthood. Coming of Age Day, however, was first celebrated in 1948, on January 15. Due to the Happy Monday System, the date was changed to the second Monday in January.