LOL Chance was humping at 9 weeks too. He started about 3 days after we brought him home! I'm not sure how to get them to stop we just redirect the behavior to something more fun and exciting, and he usually gets over it.
At this point I think it's just a dominance thing for them. I don't think it has much to do with.... you know.... hormones.
It's kinda funny though, he is so young and new at it, he actually starts humping with all four legs on the ground, before he actually goes for anyone. Then when we put him down he might have a few humps left then to.
Everyone I know said to get him neutered as soon as possible. I'm sure it will help. But I've seen dogs that still hump even after a neuter and even spay. Girl dogs do it to. Usually when playing to establish like I said dominance.