How can I delete calendar items that are a year old?
I assume you're looking to delete calendar items older than a year. The easiest way to do it is with AutoArchive.
If you want to continually and automatically prune out year-plus-old items then set your AutoArchive settings by right-clicking the Calendar folder in your Outlook Bar or Folder list. Under Properties | AutoArchive, set it to Permanently delete items older than 12 months. You'll also want to make sure that your settings under Tools | Options | Other | Autoarchive are to your liking.
If this is a one-time purging, go to File | Archive, select the Calendar folder, and tell it to archive items older than your selected date. Give it an archive filename such as "calendar purge.pst." When it completes the archive, you can simply delete that "calendar purge.pst" file from your C: drive.
A third option would be to create a calendar view that showed only appointments more than a year old: View | Current View | Define Views; use a table view and a filter to restrict the view to items more than a year old; then CTRL+A to select all of the items in the view and press DELETE to delete them all.