You cannot install WhatsApp on iOS 6, but you can use on a modern computer to message. This does not help with mobile use.
There is no "official" functional IPA for iOS 6 anymore because the servers block connections from outdated versions. Community developers sometimes create custom IPAs, such as , which attempt to restore limited functionality by wrapping the WhatsApp Web interface into an app format. whatsapp ipa ios 6
Historically, users have bypassed the "update required" screen by jailbreaking their device and using to change the SystemVersion.plist You cannot install WhatsApp on iOS 6, but