displaying age (by mnth)

[jansky]

To all guru

How can i compute for the month instead of displaying the date should display how old is it
ex: -1month +1month -2months +2months and so on

here is the age bracket
-1month (15 days but not exceed 28 days upon approval)
+1month( 28 days but not exceed 15 days for the following month)
-2month ( 15 days from the last month +15 days for the current month)
+2months ( 15 days from the current month +15 days for the following month)

Thank you