I use emacs org-mode to manage work items. Every week, I manually remove all Done items older than 2 weeks. Is there an easy way to perform this automatically?

EDIT:

I am currently trying to add a new custom command like this:

(setq org-agenda-custom-commands
  '(("P" "Show old entries" todo "DONE"
     (
      (org-agenda-files '("c:/git/org/tickets.org"))
      (tags "CLOSED<=\"-2w\"")
     )
    ))
  )

The filter on the CLOSED timestamp is not working correctly.