Android Police received a rumor that claims Google is no longer certifying new Android devices with older versions of the operating system. According to the report, February 1, 2014 was the cut-off date to certify devices with Android 4.1 (API level 16) or below. What this means is that hardware makers are no longer allowed to use these versions of Android if they want their hardware to ship with Google Mobile Services (Play Store, Gmail, Google Now, etc.)
The table below contains the approval window for Google Mobile Services (GMS). The window to certify new devices with Android 4.1 or below expired at the beginning of this month and this moves to Android 4.2 by April 24, 2014. On July 31st, device makers will only allowed to use GMS on devices with Android 4.4 or above.
The wording in this statement is important - "each platform release will have a 'GMS approval window'" - this implies that the window did not formally exist, at least in writing, prior to this announcement. The 9 month window Google is giving manufacturers before deprecating older releases also changes things. From later this year on out, it means no OEM can certify a device more than two versions behind the current Android release. Google typically releases two Android versions resulting in an API level increase per year, roughly 6 months apart, so that does mean there will be a small 3 month window where devices 2 versions behind the currently announced version could be certified. That is, unless Google plans to slow the release cycle of Android OS / API level updates.
One thing to take in mind though is that these dates are about the GMS approval process, not hardware release dates. For instance, a device that gets approved for Android 4.2 on April 23rd might not even be released until September or October.