Yes even if you're allergic to penicillin you can still safely eat blue cheese.
My mother is allergic to penicillin and she safely eats blue cheese a lot and has had not allergic reaction to it.
Although the main culture used to make blue cheese blue, Penicillium roqueforti, is the same culture that produces penicillin the enzymes that are present in the cheese break down the penicillin and render it neutral, thereby making the blue cheese safe to eat for those that are allergic to penicillin.
However some people may have an allergic reaction if they consume too much of it.
So you should start eating just a little bit of the blue cheese to see how your body reacts to it.
But my mother who is allergic to penicillin eats blue cheese without any allergic reactions or health issues.