You cannot use the latest version. You need a legacy version. The last relatively stable version for Android 2.3 is roughly (or similar builds from late 2016).
For those who absolutely must keep an Android 2.3.6 device alive: android 2.3 6 whatsapp download
If the device has a browser that supports "Desktop Mode," you might attempt to use WhatsApp Web. You cannot use the latest version
: Even if you have an old version of the app already installed, it will likely fail to connect to WhatsApp servers or display an "outdated version" error that cannot be bypassed. WhatsApp Help Center Why You Can't Download It Today android 2.3 6 whatsapp download