If you believe that people that were born on the last day of February on a leap year turn a year older on the last day of February on non-leap years, this appears to work although I'll admit that I've not tested very many possibilities.

DECLARE @DOB DATETIME

,@Now DATETIME

SELECT @DOB = '2000-02-29'

,@Now = '2001-02-28'

SELECT DATEDIFF(yy,@DOB,@Now)

- CASE

WHEN @Now < DATEADD(yy,DATEDIFF(yy,@DOB,@Now),@DOB)

THEN 1

ELSE 0

END

;