Mine was a nibbler when he was a kitten, too. And, as others have said, it's because he was weaned too early. He usually went for the toes or the nose, and he was an eye-sniffer, too! He's still a bit more bite-y than most other cats I've had, but isn't nearly as bad as when he was a kitten. And he's always very gentle.
Don't worry! They do outgrow it!