How to calculate age (in years) based on Date of Birth and getDate()

Question

I have a table listing people along with their date of birth (currently a nvarchar(25))

How can I convert that to a date, and then calculate their age in years?

Answer 1

CASE WHEN datepart(MM, getdate()) < datepart(MM, BIRTHDATE) THEN ((datepart(YYYY, getdate()) - datepart(YYYY, BIRTH_DATE)) -1 )
     ELSE 
        CASE WHEN datepart(MM, getdate()) = datepart(MM, BIRTHDATE)
            THEN 
                CASE WHEN datepart(DD, getdate()) < datepart(DD, BIRTHDATE) THEN ((datepart(YYYY, getdate()) - datepart(YYYY, BIRTHDATE)) -1 )
                    ELSE (datepart(YYYY, getdate()) - datepart(YYYY, BIRTHDATE))
                END
        ELSE (datepart(YYYY, getdate()) - datepart(YYYY, BIRTHDATE)) END            
    END