According to an update in the FAQ section of the WhatsApp app, it has now been extended to June 30, 2017.
The update reads thus:
As announced in our blog, we will soon be ending support for certain devices. On June 30, 2017, we will no longer support the following platforms:
BlackBerry OS and BlackBerry 10
Nokia S40 Nokia Symbian S60.
The following platforms will no longer be supported at the beginning of 2017:
Android 2.1 and Android 2.2
Windows Phone 7
iPhone 3GS/iOS 6
These platforms don't offer the kind of capabilities we need to expand our app's features in the future.
If you use one of these affected mobile devices, we recommend upgrading to a newer Android running OS 2.3+, a Windows Phone 8+, or an iPhone running iOS 7+ before the end of 2016 to continue using WhatsApp.