Can Airplay from Macbook on Apple TV but not Airplay Mirroring

Hi Apple community. I am running OSX 10.8.5 on Macbook pro and have Apple TV Model A1842 (32GB) tvOS 11.3 (15L211). Good signal strength on wi-fi network to both devices. Followed all the forums and suggestions to get Airplay mirroring but no joy. As mentioned in the title I can play from iTunes (movies and music) but cannot mirror screen onto the HDTV. Getting old and need a bigger screen to write emails etc.

Am reluctant to update to High Sierra as am running Microsoft 2011 and very happy with it.

Forums claim Mountain Lion OS X is compatible anyhow.

Anyone have any suggestions?