I think that how you approach your starting of your lab depends on what you want out of them. if the dog is mainly going to be retriving... Does your dog have a strong drive to retrieve already? If you are going to be using your lab for pheasant have you introduced any of the elements of it in play?

We started our lab late but we played fetch all the time and made a game out of hinding pheasent sent and such on the week ends so when we finnaly did hunt with him and train for it it was a breeze. We also have a GSP now and she took to it very early so the 3 year old lab and her hunt together very well now.