I found information on how I created a clean Calendar in January of 2012 when using an older version of OS (probably Lion) and Calendar.
Selected backup option (now only have export or archive as available options)
set prefs to clear older than x days (no options now possible to do this)
repopen and unchecked the prefs
I have now created a new calendar by the extremely tedious process of deleting over 1000 entries in the 2012 calendar one at a time.
This is a really big flaw in the current Calendar not allowing the easy creation of a new Calendar as was possible just a year ago!!!!! This was possibe every year since we got iCal until now.
Oh dear that sounds terrible. Have you submitted feedback to Apple? Maybe you should. I'm pretty sure I remember seeing that optiopn to clear older days. Don't have a clue as to why they would remove a feature like that. When I was trying to help you that was what I was looking for...
Anyway glad you got it sorted.