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.
The AGS thread about the Mac Interpreter: http://www.bigbluecup.com/yabb/index.php?topic=30021.0
The 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.