Create a query using the Criteria to include Birth Date rather than Age.  Age is a calculated field and not held as a constant in Raiser's Edge - the Age value changes depending on the constant birth date.

To resolve this error:
  1. Create a Constituent query
     
  2. On the Criteria tab, select the following fields:
    Relationships, Individuals, Birth date between [date range to include correct ages]
     
  3. To see the relationships' names and ages/birth date, select the following fields on the Output tab:
    Relationships, Individuals, Name
    Relationships, Individuals, Age
    Relationships, Individuals, Birth date
     
  4. Click Run Now