Try this in SQL.
DECLARE @BirthDay smalldatetime
SET @BirthDay = '2011-08-21'
SELECT DATEDIFF(day, CURRENT_TIMESTAMP, DATEADD(year, DATEDIFF(year, @BirthDay, CURRENT_TIMESTAMP)
+ CASE WHEN DATEADD(year, DATEDIFF(year, @BirthDay, CURRENT_TIMESTAMP), @BirthDay) < CURRENT_TIMESTAMP
THEN 1 ELSE 0 END, @BirthDay))