Yes Humping at that age is usually a dominance thing, I have a male yorkie and he hardly humped at all before being neutered. I have a female maltipoo and she humped quite abit when she was really little, she is two now and doesnt do it anymore. Also my Mothers female poodle who is spayed and 9 years old still humps if you give her a large stuffed animal. So this is normal and really has nothing to do with their sex but dominance
