How To: Exchange 2007 Reporting: Find number/ Size of emails from specific date

Since moving to exchange 2007 the size of my information stores has increased drastically, and I was looking to generate a report that would give me information as to how many emails/ total size of these emails that were older than say 1 year. This info is going to be used in a report that will be submitted to management so that an effective policy can be developed for email retention.
I've looked at things like get-mailboxstatistics and export-mailbox commands and I don't see how i would do a where clause that would generate a report giving me this information.
In Exchange 2000 and 2003 you could generate a report like this via a managed mailbox policy, but that doesn't seem to exist in this version of exchange.
I've looked at MOM briefly and i don't see where this information would be generated either.
If there are any tools in Exchange, MOM or somewhere else that could generate this info please let me know.

Any help would be appreciated.