Pulling Max (date) Not Correct

Code:
SELECT P.ID, P.QTY, T_DATE
FROM PARTS P
INNER JOIN INVENTORY I ON P.ID = I.PART_ID
WHERE P.QTY > 0 AND I.CODE = 'R'
GROUP BY P.ID, P.QTY, I.T_DATE
HAVING MAX(T_DATE) !> DATEADD(MONTH,-12,GETDATE())

[Code] ....

I am trying to make the sql only pull records where the highest date stored is older than a year ago.

So, based on today's date 12/21/2012:

if the highest (max) T_DATE is 3/12/2012 => don't pull that record
if the highest (max) T_DATE is 11/30/2011 => pull that record into the recordset

the statement is off, it is pulling records that should not be included.