Depending on what you want to use the 'age' result for there may be neater ways to do it than that calculation. However your problem is probably caused by setting that calculation field's storage to be 'On'. Turn it off and leave it to 'Recalculate when required'.
For age, I set up a calaculation field using this calculation. DOB is a date field for thier birthday.
Case ( DOB and Get ( CurrentDate ) ; Year ( Get ( CurrentDate ) ) - Year ( DOB ) - ( DayOfYear (Get ( CurrentDate ) ) < DayOfYear ( DOB ) ) )
The result should be set to number and as Sorbs said, make sure the storage is turned off to recalculate as needed.
Thank you both for your help.