How to add Inbox subfolders to Recipient Policy?

Have you selected the "All Other Mail Folders" in the policy?
Mailbox-Cleanup.jpg

I have tested this. It works for subfolders at the root of the mailbox, but not for subfolders under the Inbox. Thanks.

Well technically this should work.  You can specify specific folders, but I don't imagine your users are good enough to make subfolders with the same names across the board, but if you want to - read this:
http://exchangepedia.com/blog/2007/01/applying-mailbox-manager-policies-to.html
There is also a previous EE question with the same answer as me!
http://www.experts-exchange.com/Microsoft/Applications/Q_22961149.html
Have you applied all the latest patches / updates to your server?
What version of Exchange are you running?

I have a follow up question that might clear up some confusion. Is the "Age (days)" setting based upon actual age of the email, or the date the email was placed in a particular folder?

We are running Exchange 2003

Thanks for the help. It is the date the item was placed int eh folder. Thats what threw me off when it didn't work. All Other Folders works as it should. Thanks!

Good stuff - sounds like you know what to look for now and that it is working, albeit not quite how you were expecting it to.
Let's hope your users don't cotton on and start moving their emails around from folder to folder on a regular basis ;-)

Thanks for that tidbit hypercat - very useful.

Thank you both. I was able to test this and now understand the Age property.