I have one doubt in sql

Question

hi,

anyone help me how can i calculate the age in my table using sql 

what can i query written i will send one image please note that 

ALTER TABLE Student ADD Age AS DATEDIFF(YEAR, DateOfBirth, GETDATE())

this query can be written in my table 

my problem is i will insert new record at dob column is ;1983-11-16' so it display age as 35 

but iam checking age calculator website it display 34 

correct answer is 34 i know what query can be written in sql become as 34 please help me