Whatsapp not installing after factory reset
Here is the newest version of WhatsApp I found that is compatible with Android 2.3.3+ (WhatsApp Messenger 2.16.382)

https://www.apkmirror.com/apk/whatsapp-inc/whatsapp/whatsapp-2-16-382-release/whatsapp-messenger-2-16-382-android-apk-download/

I suspect since your phone is old, you will need the x86 arch variant.