I've been told that my forearms are too big. I have 20" arms, but due to my forearm size, my bu's don't appear as big in certain poses.
With that being said, I never train forearms. I only use straps (Versa Gripps) on back training day. So I guess bare handing the weights all these years, working construction at a young age, the creation of internet porn, and hormone use are all what contribute to my forearm size. I do think though that forearms are like calves in terms of how much genetics play a roll with them.