I'm with Gretchen that our pups are never too old to go to dog class. And WE are never too old to learn how to teach our dogs and learn to be their leader with the help of the routine of the classes. I love the prong but found it works best in conjunction with classes so it's actually a teaching aid.
In the meantime, I really do like the Gentle Leader Harness just for walking and to help with the general pulling. It's NOT really teaching them not to pull though (so you need the classes). It is giving you a break while you are learning how to work with your dog thru the classes.