Is there not a Fn key on your keyboard so render would be Fn+F12 or in System Preferences / Keyboard select the
‘Use all F1 etc keys as standard function keys’ (OSX Lion but the option is there for previous versions)
or easiest way just press the Render Image button
I don’t have a macbook Air so I’m not sure of the keyboard config but…
If you’re like me and uses the F1 to F12 for your media shortcuts, screen luminescence, dashboard etc. You could have a hard time selecting the ‘‘F’’ keys for specific Apps. On every Mac keyboard (that I know of) there is a ‘‘fn’’ key. Press fn + F12 in blender and you should have a rendered image.
By default on the newer macs, the function keys run apple-specific macros (pause/play itunes, for instance). If you intend to use extensive hotkeys in ANY app, I strongly suggest you turn all that stuff off immediately. Go into system prefs --> Keyboard and check the box that reads “Use all F1, F2, etc keys as standard function keys”