I had a caerphilly that I aged for about 3 months that was a touch bitter. However, over the time that I ate it that seemed to clear up. The bitterness was noticable, especially to me, but not overly strong and the cheese was edible. Generally, the cheeses I've had with some bitterness tended to resolve themselves as I consumed them. I've wondered if the cutting of them helps clear it up? I had put it down to too much starter, but I'm not sure if that was it or if it was simply wild Geo that was causing it. I've never had one be extremely bitter (yet, I'm sure), apart from one camembert that I left to age for far too long and it just went beyond it's use by date - but that's not the same thing. If you've got a pressed cheese that is bitter, just vac seal or wax it and put it away for four or five months, then try it again. I made a gouda the end of last year, my first hard cheese, and I let it age for about 11 months before trying it. I used more renett than I do now by about 50%. It's fine, very good in fact. Whether it was bitter or not early on I don't know, but if you're worried about your gouda, just age it out for a long time. Wax it, so it doesn't take up ripening box room, and forget about it.