Auto delete previous / old events from iOS 7 Calendar?
There are two things you can do about this, one on the device and one on iCloud.com:


On the device, you can setup to sync the calendar only for the events in the past two weeks (that's the shortest duration in the past you can set it to).


Do this by going to Settings → Mail, Contacts, Calendars
Under the Calendars section, go to the Sync submenu
Select Events 2 Weeks Back

Login to iCloud.com, go to Calendar and follow Apple's help on "Delete or hide events":


  To automatically hide past events, choose Preferences from the Action pop-up menu , click Advanced, select “Hide events n-days after they’ve passed,” then enter a number of days. 


Set it to 1 day (that's the minimum allowed).