The last port to Mac of AGS was a beta of 2.71, and Quest for Glory was made on 2.72. If you manage to add the 2.72 changes to the Mac interpreter (which is in need of a maintainer), you will be able to run not only Quest for Glory, but many other AGS games.
Edit:
The AGS thread about the Mac Interpreter:
http://www.bigbluecup.com/yabb/index.php?topic=30021.0The link to actually download the interpreter in that thread is broken, but you can download it from
here. Note that it is an interpreter, not an editor. You won't be able to do games with it, only run them. It will be easier to code, or at least I expect so.