Is there any way to know when moldy cheese (in my case, Gorgonzola) is no longer good to eat, without trying it? Mine is about three weeks old and I really can't tell any difference.
If it grows a grey or pink mold around the edges, or a black mold, throw it out. That's an undesirable mold. Those molds aren't usually dangerous, but they can make the cheese taste bad. With gorgonzola cheese specifically, the mold is injected in to the cheese via needle-like things, and then it grows veins from there. If a mold is a different color and it's coming from somewhere other than the veins, that is probably not a good mold. See also this question. .