This code will calculate and update the age.  Age and BirthDate are two LEs in the Form.

In Global Code
===========
stat svAge as String


Subroutine CalculateAge ( )

var vYears as Int
var vMonths as Int
var vDays as Int
var vBirthdate as date = Birthdate
vDays = @date - vBirthdate
vYears = vDays/365.25
vMonths = vDays/30

If vDays >= 365 then  
     {
           svAge = @str (vYears) + " Years"
          If @Int (vYears) = 1 then
           svAge = @Replace (svAge, "Years", "Year")
     }
Else if vDays >= 30 and vDays < 365 then      
     {
           svAge = @str (vMonths) + " Months"
        If @Int (vMonths) = 1 then
           svAge = @Replace (svAge, "Months", "Month")
     }
Else if vDays < 30 then
     {
           svAge = @str (vDays) + " Days"
        If @Int (vDays) = 1 then
           svAge = @Replace (svAge, "Days", "Day")
     }

Age = svAge

End Subroutine


In BirthDate On Element Change Event
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      CalculateAge ( )


In BirthDate On Form Entry Event
==============
If not @IsNew and @Update then
      CalculateAge ( )