Q: my macbook pro is a late 2011 model and yet it doesn't allow me to use mirroring option on apple tv. how do i fix

I've tried everything and can't seem to get it to work. The apple tv icon show up in itunes and I can stream everything to my tv through the apple tv on itunes, but it won't let me mirror my screen like it does with my iphone 4S. Everything I read says that a macbook dated early 2011 or later should work. My macbook is dated late 2011 and the icon for apple tv doesn't show in my menu bar or under system preferences>display. Please any advise would help