You can install mutt if it's not installed already and use it to delete messages older than a specified date. Assuming you have mutt setup to use the correct inbox, use the `D` command in mutt to delete messages by regular expression. When prompted to delete messages, use `~d >60d` (without quotes) for example to delete messages older than 60 days. You can use d for days, m for month, w for week, or y for years in the expression. Once this is done, simply quit mutt and save/purge.
If you're using the maildir format for your mail repository isntead of the standard mailbox/inbox format, you can of course manipulate the find command and delete messages that way since each message has it's own file.