ADD_YEARS takes a date and a number of years to add, and returns a date with the given number of years added.
In the special case that the new year doesn't contain the original date (e.g. when adding a year to the leap day 29.02.2016) the new date will have the same number of days from the beginning of the year (e.g. 01.03.2017 in the earlier example).
2000-01-01T00:00:00, so the year 18 years after the 1st January 2000.