Delete Old Post

I have a blog running on the latest WordPress installation. One category of my blog contains news posts which are automatically added from an external RSS feed. This category grows quickly, and also becomes outdated quickly. I would like a way to delete any posts that are older than 14 days from this category only. The wordpress plugin database doesn’t have anything, and the only other plug-in I’ve found (http://archive.ashwinbihari.com/archives/2005/07/13/plugin-auto-delete-posts/) doesn’t seem to work with the latest version of WordPress. Does anyone here know of a plug in that will delete post older than x days from a specified category (not all categories)?

PS: I know most people would argue that I shouldn’t delete old posts because they still attract traffic, or provide a useful archive, etc. but in this case the posts I want deleted are general news stories which are just mirrors of the original stories so I think it makes sense to delete them after so many days.