Discovering AGE Based On Date Columns

Hello.

I have three INT columns in a table that record the users birth year, month, and day.

BDAY_DAY (INT)
BDAY_YEAR (INT)
BDAY_MONTH (INT)

I'd like to include a function in my query that will return their Age in years based on these three columns.



I found this function on the internets, but I'm not sure how to build a DATETIME object using the three int date columns to pass to the function. If you could help me there it'd be most appriciated.


Create FUNCTION dbo.GetAge (@DOB datetime, @Today Datetime) RETURNS Int
AS
Begin
Declare @Age As Int
Set @Age = Year(@Today) - Year(@DOB)
If Month(@Today) < Month(@DOB)
Set @Age = @Age -1
If Month(@Today) = Month(@DOB) and Day(@Today) < Day(@DOB)
Set @Age = @Age - 1
Return @AGE
End

Usage (how do i pass the three columns into this function??)

SELECT Last_Name, First_Name, ssn, dob
FROM Employee_Data e (nolock)
WHERE Cust_Id = 'Customer1'
and dbo.GetAge(e.Date_Of_Birth, getdate()) >= 21