Iphone5S calendar not showing entries over 30 days old
By default, the iOS Calendars app only synchronizes and retains the last months’ worth of events on your device, regardless of how much data is stored in whatever cloud or desktop calendar application you’re synchronizing with. 

This can be changed in the Settings app; under the Mail, Contacts, Calendars section there is an option near the bottom to set how much of your calendar data you want synchronized and retained on your device, with options for two weeks, 1 month, 3 months, 6 months or everything regardless of how old.