DATEDIFF (datepart, start, end)
Select *, DATEDIFF(year, DOB,GETDATE()) as COLUMN_NAME from TABLE_NAME
GETDATE = CURRENT DATE
DOB = PATIENT'S DATA OF BIRTH
YEAR = FORMAT THAT WILL RETURN THE PATIENT AGE FOR EXAMPLE: 21
(IF YOU PUT MONTH INSTEAD OF YEAR , IT WILL GIVE YOU THE AGE IN MONTHS, LIKEWISE FOR DAY)
FOR EXAMPLE: YEAR = 21, MONTH = 252, DAY = 7665