Definitely get him neutered. He isn't too old to stop that habit, and you should stop him when he starts to hump - if you haven't attended obedience classes, that would be helpful to start so that you could teach commands like "leave it" and "off" but right now his hormones are dictating his behavior and that needs to be done. It is an easy procedure for males, and they are back to their old selves within a day or two. Once the hormones settle down, he will be receptive to training and the air humping will go away!
