If we are discussing the actual deleted items folder - this is, I believe, regularly cleaned at the server end. it may be possible to set this cycle time in the server settings in your profile
if you wish to keep older mails - create a folder (or several) and move from the inbox to the new folder
the deleted items folder is a last chance to recover any accidentally deleted items before they are permanently deleted.
Hotmail uses a system similar to the IMAP standard but which uses a proprietary Microsoft system, to sync the local and server copies