I also don't know anything about the sport, but would advise that you talk to your vet and have the dog given a clean bill of health before you start a new thing with him. Then, as Ownerof3dogs suggests, you will need to build up his muscles for the activity. That's okay, you'll probably have to build up your own as well. I seriously doubt he's too small or too old to go out and "play" with Mom. If the skijoring doesn't work out after you teach him to pull, he could still pull a small wagon around or something like that and be the neighborhood dog taxi. I'll bet he'll enjoy the challenge of something new and as long as you have no dysplagia problems or other skeleto-muscular problems you'll probably have a great time together. Keep us posted on how you make out.