I wish to create an email filter rule that trashes email when it's two weeks old. The date conditions seem to force me into selecting a specific date instead of just evaluating how many days old a message might be. Is anyone able to describe how to set up such a rule?
There is no way to do what you are describing in the webmail UI. Emails remain in the Inbox or other folders until you delete them yourself, except for the Spam and Trash folders. Those deletion schedules cannot be modified. You would need to enable the account in a client like Thunderbird, which appears to have that capability. Other clients may have it too.