As a side effect of the version fragmentation that Android suffers from, even the latest apps tend to support Android versions a few years old. For example, most of Google's apps nowadays have a minimum requirement of Android 4.1 or 4.2. If you're still stuck on 2.3 Gingerbread, at least you'll get to keep using WhatsApp.
Last year, WhatsApp said it was ending support for a variety of older mobile operating systems, like iOS 6 and Android 2.2 (and below). The blog post announcing this change has been updated, with changed dates for some versions. Now WhatsApp says that Android 2.3.7 and older will continue to work until February 1, 2020.
The post isn't clear if Android 2.1 and 2.2 support is still being dropped, but Gingerbread users should be able to continue using WhatsApp for a few more years. I can't imagine anyone will be using Android 2.3 by that time, but I'm sure that's what Microsoft kept saying about Windows XP (which just received a security patch earlier this month).