Before we knew better, we brought Neo home at 6-7 weeks old. He humped his blankie as soon as we were home! He humped everything he could get hold of! It was so funny we even bought him a stuffed "Phucky Duck", lol. The vet told us that is actually was healthy for him to do it, as it helped to "seat" his testicles. Neo was neutered at 8 months and even though he does it much less now, he still has the urge. I wouldn't worry about it too much.
