Male cat & a female kitten

Question
I have a siamese neutered male cat age 4 years named Mojo and just brought home an 8 week old female kitten named Kiki. Within a matter of hours Mojo and Kiki became friends,and Mojo constantly grooms her. They share potty boxes and eat together, and play alot. If the kitten is in distress, Mojo runs over to help her.
Lately, I've noticed him biting her neck and meowing at her. She stays still, then meows and manages to get cut loose from, and then resumes playing. Mojo seems to be biting her neck more these days, and his meowing has become intense. but when I walk in the room, he seems okay and wags his tail, and they both play again. I am assuming he is training her to "calm down" as she gets out of hand. The vet thought that he was very attached to her in such a short time but didn't see it as a problem. They came together in one carry box to the vet and they both seemed fine in and out of doctor's office. Is Mojo okay? I keep them separate at night because I can't monitor him especially when he is clamping down on her neck. I prefer they sleep! Let me know what you think. They are both healthy.

Answer
Ana,

How long ago did you get the kitten?  Do you know Kiki was really only 8 weeks old when you got her.  I have heard of kittens coming into season as young as 16 weeks of age.  

Anyway, the behavior is not harmful and speculate though we might, it is not clear to me what it means.  If she is in season, even though he is neutered, he may engage in mating behaviors.

Best regards... Norm.