shredding attachments based on date

Hi all, 

  I'd like to remove attachments older than x months from the database
and thought probably rt-shredder is the tool for this (its not something
I've used before). Having googled this a bit and checked "rt-shredder
--plugin help-Attachments" for instructions it looks like it may not be
possible to use date, can anyone advise? Otherwise I guess I need to
delete them directly from MySQL, not sure if this will make a mess of RT
though, 

thanks for any help, Andy.