iOS contains a setting that allows you to synchronize various intervals of past calendar events to your device.  The setting intervals, as well as the steps for changing the interval, are provided below:

• Events 2 Weeks Back

• Events 1 Month Back

• Events 3 Months Back

• Events 6 Months Back

• All Events

1.  From the home page, tap Settings.

2.  Tap Mail, Contacts, Calendars.

3.  Under the CALENDARS section, tap the Sync option.

4.  Choose the desired interval.