I forget who I got this one from but I've never found anything simpler for correctly calculating age in years. Using Lynn's good test harness...

CREATE TABLE #T(Id INT,date1 DATETIME,date2 DATETIME)

INSERT INTO #T

SELECT 1,'2/1/2007','1/31/2010' UNION ALL

SELECT 2,'2/1/2007','2/1/2010' UNION ALL

SELECT 3, '2/1/2007','1/15/2010' UNION ALL

SELECT 4, '2/1/2007','2/2/2010'

SELECT

Id,

date1 AS 'Start',

date2 AS 'End',

YEAR(date2 - DATEPART(dy, date1) + 1) - YEAR(date1)

FROM #T

DROP TABLE #T