Airplay mirroring not appearing

I have a late 2011 Macbook Pro (which Apple states is compatible for Apple TV/airplay mirroring). I also have updated software, etc. My problem is that I cannot use airplay on this macbook. The option doesn't even appear in the display settings (only has box for show display settings in menu). I know that our apple TV is fully functioning, as all my other devices work perfectly (Mac, iphones, ipads, etc). I also know that I am on the correct network. I've check firewalls, everything, and cannot figure out why Airplay is not available to me. Can anyone help?