In the comments to my recent blog post RSS Bandit Gets Around Phil Weber asked

Dare: In addition to manual deletion, please consider offering an option to "Automatically delete posts older than X days." Flagged posts should not be auto-deleted. Thank you!

This functionality already exists in RSS Bandit. You can set it on a per feed level and have a global default setting as well. The user interface for it is misleading which is probably why most people don't know it exists. The fields called "Max Item Age" and "Default Maximum Item Age" should actually be labelled as "Delete Items Older Than" instead. I'll probably change the text in the code after posting this blog entry.

This is a screenshot of the global settings which configures it for all currently subscribed feeds

This is a screenshot of the properties dialog for a feed where one can override the global setting