Is it possible to sync Exchange calendar more than two weeks past?
There's only that option "Download email from: the last month/any time" and that doesn't work with calendar :/
I'm seeing Calendar evenings on my Exchange 2010 mailbox as far back as September 28, 2012. From what I have found, it looks like three months may be the "built-in" limit for WP8, and it might simply be that the Exchange server you are syncing with has an ActiveSync Mailbox Policy that is limiting to only two weeks prior.
It also appears that if you are synching Google or Outlook.com events those will only sync two-weeks worth of previous events as well.