I just wanted to post a quick tip a way to resolve the error “The build host is too old for this version of Xamarin.iOS extension” in Visual Studio. This seems to occur if you recently set up a proxy of some sorts or have installed a tool like Fiddler.
I had just installed Fiddler to capture HTTP packets for monitoring my requests and responses when communicating with a back-end. Turns out Fiddler had enabled a proxy of a sort that disrupts the Xamarin Build host connection into thinking that the build host is too old.
Opening up Fiddler and turning off all the Proxy-settings I could find, the connection was fixed and I could build again. Happy days.