Working
The calculator measures from the earlier date of birth to the later one: full calendar years first, then full months, then the remaining days.
18 Jul 1982 → 18 Jul 1992 = 10 years
18 Jul 1992 → 18 Aug 1992 = 1 month
18 Aug 1992 → 16 Sep 1992 = 29 days
Age gap = 10 years, 1 month and 29 days = 3,713 total days.