Apple TV (third generation) will further not be able to stream YouTube. The older Apple TV model will require an AirPlay to play YouTube videos. However, the recent Apple TV HD and Apple TV 4K are not affected.
The only possible method to run YouTube on the older model is to use AirPlay function while using an iPad or iPhone.
A popup message has appeared on the older Apple TV, that is
Starting early March, the YouTube app will no longer be available on Apple TV (3rd generation). You can still watch YouTube on Apple TV 4K, Apple TV HD, iPhone, or iPad. With AirPlay, you can also stream YouTube from your iOS device directly to any Apple TV (3rd generation or later).
So if you are a user of Old Apple TV, you have just got two options; first, use AirPlay feature using your iPhone or iPad. The second one is, you have to switch to another possible streaming device. As many TV’s nowadays have their built-in apps like YouTube, Netflix etc. In my opinion Amazon Fire Tv Stick 4K and Roku TV Ultra are also the best choices to go for.