Jorge Solá 2/6/2017 6:07:30 PM
This is what the formula does, for instance, with someone born on December 15, 1975.
1) Calculates the difference in years between the present year & the year of birth (2017-1975=42)
2) It adds this number of years to the date of birth with the AdjustYear formula (result: December 15, 2017).
3) If the resulting date is in the future (the person didn't yet have their birthday this year), it takes the number in 1) & substracts 1.
4) If the resulting date is today or is in the past (the person already had their birthday this year), it returns the number in 1).
So the formula is accurate to the day.