Age and member month computation

Transact-SQL
4

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select memid
      ,fullname
      ,dob
      ,sex
      ,enrollid
      ,enrolleffdate
      ,enrolltermdate
      ,(datediff(month,dob,enrolleffdate)+1)/12 as age
      ,case
          when (datediff(month,dob,enrolleffdate)+1)/12<21
          then 0
          else datediff(month,enrolleffdate,enrolltermdate)
       end as membermonth
  from @memage
;