How far in the future can I create events on my calendar? My calendar does not accept events for September 2016 or beyond but will for May 2016.   Is there a limited time frame or horizon ?
This issue is related to the API limitations itself and vary on different platforms, device, regional settings etc. However you can get some functions blocked if you create to many events or calendars in short period of time.

Google: https://support.google.com/a/answer/2905486?hl=en

iCal: support.apple.com/en-us/HT202158

How to Hit the limits of Google calendar:


  If a user sees one of these messages it’s probably due to one of the
  following reasons:

Creating too many events

If a user has created more than 10,000 events in his or her calendar within a short period of time, that user might lose calendar edit access.

Creating too many calendars

If a user creates more than 25 new calendars within a short period of time, that user's calendar might go into read-only mode.

Sending too many invitations or emails to external guests

In order to prevent spamming, Google Calendar limits the number of invitations a user can send to external guests. This limit varies

  
  depending on the action, and is usually between 100-300 guests.

Google Apps users can send invitations to any number of guests from their primary domain, or from secondary domains associated with

  
  their primary domain.

Sharing calendars with too many users

If a user shares one or more calendars with many other users within a short period of time, Google Calendar might switch into

  
  read-only mode for that user. It’s almost impossible to reach this
  limit by updating sharing settings manually, but it can happen with
  some API-based tools or third-party apps.