KGuest did you ever solve this? I have a mid 2012 MacAir and Apple TV by all accounts model and software are current but no Airplay symbol appears in iTunes as per instructions:
To stream music or videos from your computer to an Apple TV or AirPort Express:
- Connect your computer and Apple TV to the same Wi-Fi network.
- Open iTunes (10.2 or later).
- Locate and click the icon in the bottom-right corner of the iTunes application.
Can't find symbol, super frustrustating!!!!!