I wondered if you had a cockerdile!
Both my cocker and my current spaniel mouthed and nipped until quite late, the first one had me in despair, and both by the time they passed out of their wild teens were absolutely trustworthy and had the softest mouths imaginable. It does pass, and I wonder sometimes if its because they end up learning so much about mouth sensitivity that they're utter nightmares when young.
Often both of mine were vile and bitey monsters when tired, and while my girl figured out by about 9 months old how to switch herself off and rest when tired, my boy was still going crazy and needing to go in his crate to find his off button until he was about 13 months old. He used to hit the red zone about 7pm and be impossible. I went back to very strict eat, play, nap schedules like I did when they were puppies, rested them a whole lot more, and was really clear with both of them about ouch, no, ignore. But most of it was overtiredness and immaturity.
The best advice I was ever given was by a working cocker owner who owned a highly challenging, high speed rocket, who taught me to spot the signs that the pup needs a treat to take in the crate and a nap.
My raving maniac is asleep on my lap right now, it really does pass.