How do I put a datediff with case in a sql where clause

Hello Experts,

Hope you are all keeping well.

Here is what I would like in the where clause of a sql select statement:

DATEDIFF(YY,GAC.BIRTHDATE,GETDATE()) - CASE WHEN DATEADD(YY,DATEDIFF(YY,GAC.BIRTHDATE,TERM.TERM_BEGIN_DT),GAC.BIRTHDATE) > TERM.TERM_BEGIN_DT THEN 1 ELSE 0 END

how do I do this ?  

thanks, Brock