This has been submitted as an enhancement request in the ideas section, in the mean time, for anyone searching through here looking for a temporary solution, here are a couple of ideas that may work in some Exchange environments to simplify the removal of those old emails.
1. Exchange Server Export-Mailbox PowerShell Cmdlet: Schedule/Script this CmdLet to remove emails older than...
Export-Mailbox -Identity “MailboxNameGoesHere″ -IncludeFolders "\Inbox", “\Sent Items”, “\Deleted Items” -StartDate “1/1/2012″ -EndDate “1/1/2022″ –DeleteContent
2. Exchange Retention Policy: Use Exchange "Retention Policies" to set a policy on the specified mailbox/mailboxes that removes emails that are older than "x" days. This may be something only available in relatively newer versions of Exchange.