When using Outlook.com, that is accessed from the metro tile, it says beneath the mail header column "To get mail older than 2 weeks go to settings." I assume they mean the charms settings. I go to accounts and options and see no option for getting mail older than 2 weeks.
you almost got it. with the mail app open, go to the charms bar and then settings. click or tap "Accounts" and then click/tap on your account (outlook.com, hotmail.com, yahoo.com, etc.). then change the "Download Email From" and change it from the default 2 weeks to "anytime"
Jack