WORKINGDIR "c:\folder\to\clean"
SET temp = %datetime
DATETIMESUB temp 30 /day 
SET thirty_days_ago = temp
:loop
GETNEXTFILE "*" /oldest 
IFERROR RETURN $ERROR_SUCCESS
IFDATETIME> %nextfiledatetime thirty_days_ago RETURN $ERROR_SUCCESS
;; File is more than 30 days old, so delete it
DELETE %nextfile
;; It's a good idea to make sure the delete doesn't fail due
;; to a permissions issue (want to avoid getting stuck in
;; an infinite loop).
IFERROR RETURN
GOTO loop