Humping at the Dog Park

Despite being neutered, Loki is now starting to hump. Over 6 months of age, starting to hump. Isn't that a bit early? Especially for a neutered dog? We sure got a dominant dog on our hands. He's really testing his boundaries and being quite bold. I don't have much more to say, because it was Yun who took Loki to the dog park this time.