Date calculations are not that difficult, for FM a date is a number.
Just don-t use the 'Today', but the Get(CurrentDate) function.
Get(CurrentDate) - date of birth will give you the days between those two dates.
This will give you the days 'between', so you will have to add 1 day for an 'age', depend how your definition for age is.
To get the weeks you have to devide by 7 (7 days in a week)
This will give you a clumsy number x,yyyy.
So, we take the integer in one field and the modulo in an other field:
Int((Get(CurrentDate)-date of birth)/7)for the rest days and
Mod( (Get(CurrentDate - date date of birth), 7)for the week(s)
Play with the +1 to get close to your definition of age and make sure the calculation result is number, unstored.
HTH