Google has decided to disallow new device/account activations of the Google Sync (Microsoft Exchange ActiveSync) method of connecting to free Gmail or Google Apps Mail accounts.
They had said that the deadline for iOS and Windows Phone devices was going to be January 30th, and then backed off of that deadline for Windows Phone users until July, I believe, because they do not yet have a native GMail App released for Windows Phone.
The January 30th deadline came and went, and Google was still activating new device/account combinations to the ActiveSync servers, so there was speculation that they had quietly let the overall deadline slip, but it appears that just yesterday they started enforcing the new policy and new device/account activations can no longer be made for free gmail/google apps mail accounts.
Note, that if you already had a given device using ActiveSync to connect to a given gmail account, it is expected that the free connection will remain for the life of that device.
In order to access GMail now from iOS devices, you have to either set up an SMTP based connection to GMail in the iOS native app, or download and use the GMail app from google.
Lots of details are in the thread over in the iOS 6 forum.
https://forums.macrumors.com/threads/1534449/