The rescue I work through is six months. Before that they call it microscopic surgery. Another vet I've used says 2 pounds. It really varies greatly from vet to vet. Personally I wait till six months for all of the ones I've had done.
Has Gizmo got a couple of stuffed toys (our size, not his) that you can give him when he starts using your hand/arm to play roughly? That may be enough to divert his attention. He really is just being a bratty boy. I have a few of them myself right now.
The other way of course for him to not use you for his personal play toy is to get him a playmate. That way they will be busy playing with each other and will leave you alone.
