This logo was used from iPhone OS 1 to iOS 5. The default YouTube app was removed in iOS 6. The service in that app was still functional until April 2015, when V2 of the YouTube Data API ceased to function.
App Store version
After the default YouTube app was removed in iOS 6, the YouTube app from Google was available on the App Store since the release of iOS 6 in late 2012. This logo was used from version 1.0 to 2.0, on iOS 4 to 7.0.6.
This logo was used from version 2.0 to 10.38, on iOS 7.1 to 9.
In 2015, YouTube inversed the colors, and added some shadows in the triangle and in the rectangle and the app frame. This logo was used from version 10.38 onwards, on iOS 9 onwards.
In 2017, YouTube changed the iOS icon after it changed it's logo, not a lot of changes, they only deleted the shadows of the last version. This logo is from iOS 9 and onwards