Get age group as specified in table lk_AgeGroup (which may be customised by the user). The table values are read once and then cached for the lifetime of the application. The makes the lookup very fast.
Returns an AgeGroup_ID from the table. -10 is the fixed 'Unknown' group.
Either Null or the Date of Birth as a Date or String.
The optional date at which to calculate age. Defaults to today.
GetAgeGroup ("21 Sep 1970", #1 Jan 2014#) => 44