Probably not.
I bought it on Steam and tried it. No go. The game wouldn't even launch. It presented me with a pop-up saying it couldn't run on my Mac.
My iMac is the same vintage as yours, with the GT 650M GPU.
Yup. I already posted my experience on another thread awhile ago. However, you CAN launch it by clicking on "show package content", and then navigating to contents/MacOS (or something like that), and then clicking on executable file.
The intro and credits will be slideshow. But afterwards the game itself should run fine in medium settings.... until you light up the flare. The game will just quit whenever the flare is lit! I guess the game should run fine if you somehow can get through the entire game without flare.
I am seriously considering a Retina iMac now...