My adult male keeps humping female puppy!

So I brought home a puppy about 2 weeks ago so that my 10 yr old male pit/boxer has a playmate. Tigger just LOVES Lexi, but maybe too much. He has just started humping her. She is only 10 weeks and 13 lbs. He is 45 lbs. He also is biting her neck and legs. I think most of it is play, but he is getting "excited" when he humps her-if you know what I mean. Should I stop this or let her fight back if she doesn't like it? She is instigating play by chomping on his face and laying on her back and kicks him with her feet. I fear he is too rough or will bit her too hard, esp. on the neck. Anyone have this problem before? My male IS fixed.