Workaround for YouTube to appear in Apple TV
YouTube has changed their API from version 2 to version 3, and on May 1st they shut down access to any program/web page or service that accessed the YouTube v2 API. This included older Apple TVs. In order to actually get a working YouTube program on his Apple TV, he will need a new one, which has an updated YouTube program using the new API.

Other than that, AirPlay is your only option. Which he doesn't seem to like.

Update: AirPlay may no longer works as a fix for this on older Apple TV's. It thinks it is playing an audio file and no picture appears on screen.