Just got both puppies fixed, one male, one female. They are 6 months old and the female went into heat. They tried mating a few days before they were fixed and we kept them separated. Even after surgery, they are still trying to mate. Thus still having to keep them separated. When will they stop this?
I own a dog and sit dogs. They often try to mate, even same sex. I think it is because they get excited to see a friend or conversely, stressed when a new dog comes to the house and want to be clear on dominance.
Every dog is different. Just being spayed or neutered doesn't always nip the desire to mate. Testosterone and estrogen (or reproductive hormones) can stay in the system for weeks or even months. The act of mounting isn't always a reproductive trait and may take some strict training to rid that habit.
Mounting, or humping, can have different meanings. Since your female was just in heat, they're still just a little hormonal, and it should subside in a week or so, if it's just due to her smelling hot. Besides hormonal, wanting to mate behavior, dogs will sometimes mount and hump each other. Any age, any gender. Sometimes it's excitement/play, and sometimes it's more of a dominance issue. The one mounting could be trying to show dominance over the other. It's easier to tell the cause of the behavior after seeing it in person, and knowing the dogs. Harder to predict when unfamiliar with the exact situation or animals.
Probably around 10-12 months. Their bodies have to take time to calm down after a massive surgery like that