It is very simple, just use the following sql statement,

(DATEDIFF(YY,DOB,GETDATE()) - CASE

WHEN MONTH(DOB)<MONTH(GETDATE()) AND (MONTH(DOB)=MONTH(GETDATE()) OR DAY(DOB)>DAY(GETDATE())) THEN 0 ELSE 1

END)

Here DOB is Columname, and GETDATE() is a function which gives the current date.