age.sql

 -- Get age from birthdate
 select (
  case when 
    datepart(year,[BirthDate])>(1900) 
    AND datepart(year,[BirthDate])<datepart(year,getdate()) 
    AND (datepart(month,[BirthDate])>=(1) 
    AND datepart(month,[BirthDate])<=(12)) 
    AND (datepart(day,[BirthDate])>=(1) 
    AND datepart(day,[BirthDate])<=(31)) 
    then 
      case isdate(CONVERT([datetime],[BirthDate],(0))) 
        when (1) 
          then floor(datediff(dayofyear,[birthdate],getdate())/(365.25)) 
        when (0) 
          then NULL  
        end  
      end) 
    as age 
 from person