Calculate Age Function

Two variations of the function but the purpose is to determine the difference in dates and display the result in one column.

IF OBJECT_ID(N'dbo.fnAge') IS NOT NULL
	DROP FUNCTION dbo.fnAge
GO

CREATE FUNCTION [dbo].[fnAge] (
	@dayOfBirth DATETIME
	,@today DATETIME
	)
RETURNS VARCHAR(100)
AS
BEGIN
	DECLARE @thisYearBirthDay DATETIME
	DECLARE @years INT
		,@months INT
		,@days INT

	SET @thisYearBirthDay = DATEADD(year, DATEDIFF(year, @dayOfBirth, @today), @dayOfBirth)
	SET @years = DATEDIFF(year, @dayOfBirth, @today) - (
			CASE
				WHEN @thisYearBirthDay > @today
					THEN 1
				ELSE 0
				END
			)
	SET @months = MONTH(@today - @thisYearBirthDay) - 1
	SET @days = DAY(@today - @thisYearBirthDay) - 1

	RETURN cast(@years AS VARCHAR(2)) + ' years,' + cast(@months AS VARCHAR(2)) + ' months,' + cast(@days AS VARCHAR(3)) + ' days'
END

SELECT dbo.fnAge('1981-09-01', GETDATE()) AS Age;

Result: 31 years,5 months,26 days

Detailed
Credit goes to armen at http://stackoverflow.com/users/395720/armen
While his response on this URL isn’t a function it is his code that makes the function work http://stackoverflow.com/questions/11184476/how-to-calculate-age-in-t-sql-with-years-months-days-hours-minutes-seconds

IF OBJECT_ID(N'dbo.fnAge') IS NOT NULL
	DROP FUNCTION dbo.fnAge
GO

CREATE FUNCTION [dbo].[fnAge] (
	@dateFrom DATETIME
	,@dateTo DATETIME
	,@datetimeoption INT
	,@displayoption INT
	)
RETURNS VARCHAR(max)
AS
BEGIN
	DECLARE @tmpdate DATETIME
	DECLARE @years INT
	DECLARE @months INT
	DECLARE @days INT
	DECLARE @hours INT
	DECLARE @minutes INT
	DECLARE @seconds INT
	DECLARE @milliseconds INT
	DECLARE @sign CHAR
	DECLARE @return VARCHAR(max)

	--SELECT @dateFrom    = '2012-02-03 11:24:38:000'
	--SELECT @dateTo      = '2013-03-04 12:25:39:003'
	SELECT @sign = '+'

	IF @dateFrom > @dateTo
	BEGIN
		SET @tmpdate = @dateFrom
		SET @dateFrom = @dateTo
		SET @dateTo = @tmpdate
		SET @sign = '-'
	END

	SELECT @tmpdate = @dateFrom

	SELECT @years = DATEDIFF(yy, @tmpdate, @dateTo) - CASE
			WHEN (DATEPART(mm, @dateFrom) > DATEPART(mm, @dateTo))
				OR (
					DATEPART(mm, @dateFrom) = DATEPART(mm, @dateTo)
					AND DATEPART(dd, @dateFrom) > DATEPART(dd, @dateTo)
					)
				OR (
					DATEPART(dd, @dateFrom) = DATEPART(dd, @dateTo)
					AND DATEPART(hh, @dateFrom) > DATEPART(hh, @dateTo)
					)
				OR (
					DATEPART(hh, @dateFrom) = DATEPART(hh, @dateTo)
					AND DATEPART(mi, @dateFrom) > DATEPART(mi, @dateTo)
					)
				OR (
					DATEPART(mi, @dateFrom) = DATEPART(mi, @dateTo)
					AND DATEPART(ss, @dateFrom) > DATEPART(ss, @dateTo)
					)
				OR (
					DATEPART(ss, @dateFrom) = DATEPART(ss, @dateTo)
					AND DATEPART(ms, @dateFrom) > DATEPART(ms, @dateTo)
					)
				THEN 1
			ELSE 0
			END

	SELECT @tmpdate = DATEADD(yy, @years, @tmpdate)

	SELECT @months = DATEDIFF(mm, @tmpdate, @dateTo) - CASE
			WHEN (DATEPART(dd, @dateFrom) > DATEPART(dd, @dateTo))
				OR (
					DATEPART(dd, @dateFrom) = DATEPART(dd, @dateTo)
					AND DATEPART(hh, @dateFrom) > DATEPART(hh, @dateTo)
					)
				OR (
					DATEPART(hh, @dateFrom) = DATEPART(hh, @dateTo)
					AND DATEPART(mi, @dateFrom) > DATEPART(mi, @dateTo)
					)
				OR (
					DATEPART(mi, @dateFrom) = DATEPART(mi, @dateTo)
					AND DATEPART(ss, @dateFrom) > DATEPART(ss, @dateTo)
					)
				OR (
					DATEPART(ss, @dateFrom) = DATEPART(ss, @dateTo)
					AND DATEPART(ms, @dateFrom) > DATEPART(ms, @dateTo)
					)
				THEN 1
			ELSE 0
			END

	SELECT @tmpdate = DATEADD(mm, @months, @tmpdate)

	SELECT @days = DATEDIFF(dd, @tmpdate, @dateTo) - CASE
			WHEN (DATEPART(hh, @dateFrom) > DATEPART(hh, @dateTo))
				OR (
					DATEPART(hh, @dateFrom) = DATEPART(hh, @dateTo)
					AND DATEPART(mi, @dateFrom) > DATEPART(mi, @dateTo)
					)
				OR (
					DATEPART(mi, @dateFrom) = DATEPART(mi, @dateTo)
					AND DATEPART(ss, @dateFrom) > DATEPART(ss, @dateTo)
					)
				OR (
					DATEPART(ss, @dateFrom) = DATEPART(ss, @dateTo)
					AND DATEPART(ms, @dateFrom) > DATEPART(ms, @dateTo)
					)
				THEN 1
			ELSE 0
			END

	SELECT @tmpdate = DATEADD(dd, @days, @tmpdate)

	SELECT @hours = DATEDIFF(hh, @tmpdate, @dateTo) - CASE
			WHEN (DATEPART(mi, @dateFrom) > DATEPART(mi, @dateTo))
				OR (
					DATEPART(mi, @dateFrom) = DATEPART(mi, @dateTo)
					AND DATEPART(ss, @dateFrom) > DATEPART(ss, @dateTo)
					)
				OR (
					DATEPART(ss, @dateFrom) = DATEPART(ss, @dateTo)
					AND DATEPART(ms, @dateFrom) > DATEPART(ms, @dateTo)
					)
				THEN 1
			ELSE 0
			END

	SELECT @tmpdate = DATEADD(hh, @hours, @tmpdate)

	SELECT @minutes = DATEDIFF(mi, @tmpdate, @dateTo) - CASE
			WHEN (DATEPART(ss, @dateFrom) > DATEPART(ss, @dateTo))
				OR (
					DATEPART(ss, @dateFrom) = DATEPART(ss, @dateTo)
					AND DATEPART(ms, @dateFrom) > DATEPART(ms, @dateTo)
					)
				THEN 1
			ELSE 0
			END

	SELECT @tmpdate = DATEADD(mi, @minutes, @tmpdate)

	SELECT @seconds = DATEDIFF(ss, @tmpdate, @dateTo) - CASE
			WHEN (DATEPART(ms, @dateFrom) > DATEPART(ms, @dateTo))
				THEN 1
			ELSE 0
			END

	SELECT @tmpdate = DATEADD(ss, @seconds, @tmpdate)

	SELECT @milliseconds = DATEDIFF(ms, @tmpdate, @dateTo)

	--SELECT
	--    @sign AS [sign]
	--    , @years AS [years]
	--    , @months AS [months]
	--    , @days AS [days]
	--    , @hours AS [hours]
	--    , @minutes AS [minutes]
	--    , @seconds AS [seconds]
	--    , @milliseconds AS [milliseconds]
	SET @return = (
			CASE
				WHEN @datetimeoption = 0
					THEN (
							CASE
								WHEN @displayoption = 0
									THEN CONVERT(VARCHAR(12), @years) + ' Year(s), ' + CONVERT(VARCHAR(12), @months) + ' Month(s), ' + CONVERT(VARCHAR(12), @days) + ' Day(s)'
								WHEN @displayoption = 1
									THEN CONVERT(VARCHAR(12), @years) + 'y ' + CONVERT(VARCHAR(12), @months) + 'm ' + CONVERT(VARCHAR(12), @days) + 'd'
								END
							)
				WHEN @datetimeoption = 1
					THEN (
							CASE
								WHEN @displayoption = 0
									THEN CONVERT(VARCHAR(12), @years) + ' Year(s), ' + CONVERT(VARCHAR(12), @months) + ' Month(s), ' + CONVERT(VARCHAR(12), @days) + ' Day(s), ' + CONVERT(VARCHAR(12), @hours) + ' Hour(s), ' + CONVERT(VARCHAR(12), @minutes) + ' Minute(s), ' + CONVERT(VARCHAR(12), @seconds) + ' Second(s), ' + CONVERT(VARCHAR(12), @milliseconds) + ' Millisecond(s)'
								WHEN @displayoption = 1
									THEN CONVERT(VARCHAR(12), @years) + 'y ' + CONVERT(VARCHAR(12), @months) + 'm ' + CONVERT(VARCHAR(12), @days) + 'd ' + CONVERT(VARCHAR(12), @hours) + 'h ' + CONVERT(VARCHAR(12), @minutes) + 'm ' + CONVERT(VARCHAR(12), @seconds) + 's ' + CONVERT(VARCHAR(12), @milliseconds) + 'ms'
								END
							)
				END
			)

	RETURN @return
END;

SELECT dbo.fnAge('1981-09-01 15:20:00', getdate(), 0, 0);
-- Result: 33 Year(s), 3 Month(s), 9 Day(s)
SELECT dbo.fnAge('1981-09-01 15:20:00', getdate(), 0, 1);
-- Result: 33y 3m 9d
SELECT dbo.fnAge('1981-09-01 15:20:00', getdate(), 1, 0);
-- Result: 33 Year(s), 3 Month(s), 9 Day(s), 18 Hour(s), 34 Minute(s), 26 Second(s), 476 Millisecond(s)
SELECT dbo.fnAge('1981-09-01 15:20:00', getdate(), 1, 1);
-- Result: 33y 3m 9d 18h 34m 26s 476ms