In this page, you can calculate age difference by simply entering two individuals birthdate. There is no particular order to enter their birthdates.
Example, if you are checking age difference for marriage, if bride's date of birth is, 04-03-2005 and groom's date of birth is 03-11-1996, then select person 1's dob with 1996 as year, November as month and select 03 as day. Similarly, for person 2, select 2005 as year, march as month and 04 as day.
In this tool, you can also check the exact age to this date.