"Age is a flat classification with single-year categories from 0 years to 119 years inclusive, plus a category for 120 years and over. Classifications for date of birth are required because age is derived from the day, month and year a person is born. Date of birth is derived from three flat classifications: date of birth day, date of birth month and date of birth year. Day has single categories 01 to 31 (representing the days of the month). Month has single categories 01 to 12 (representing the months of the year). Year has single categories (representing 120 years back from the current year). For example, in 2007, the year classification range starts with 1887, which is 120 years from 2007."