Create function to calculate age on specific date

 This function will take 2 datetime parameters, the DOB, and a date to check the age at.

CREATE FUNCTION [dbo].[Calc_Age]
(
@DOB datetime , @calcDate datetime
)
RETURNS int
AS
BEGIN
declare @age int
IF (@calcDate < @DOB )
RETURN -1
-- If a DOB is supplied after the comparison date, then return -1
SELECT @age = YEAR(@calcDate) - YEAR(@DOB) +
CASE WHEN DATEADD(year,YEAR(@calcDate) - YEAR(@DOB)
,@DOB) > @calcDate THEN -1 ELSE 0 END
RETURN @age
END

Check the age:

SELECT dbo.Calc_Age('2010-04-13',Getdate())

Output

11