to Accurately calcutalte the age of something this works for most situations
SELECT
FLOOR( --floor function returns age in years
CAST( DATEDIFF( DAY, /*StartDate*/ , /*EndDate*/ ) AS DEC(38,16) ) / CAST(365.2425 AS DEC(38,16))
) As AgeInYears
FROM SomeTable
calculate age from current date using GETDATE
SELECT
FLOOR( CAST( DATEDIFF( DAY, e.BirthDate , GETDATE() ) AS DEC(38,16) ) / CAST(365.2425 AS DEC(38,16)) ) As AgeInYears
FROM Employees AS e
Calculate age from a specific date using DATEFROMPARTS
SELECT
FLOOR( CAST( DATEDIFF( DAY, p.ReleaseDate , DATEFROMPARTS(3030,3,11) ) AS DEC(38,16) ) / CAST(365.2425 AS DEC(38,16)) ) As AgeInYears
FROM Products as p