Your pup may not be ready or understand what hunting is yet. Keep taking them outdoors and encourage the pup to range and explore. You can help the pup along by buying a small bird like quail and have it struggling around. Do that by pulling wing feathers and tying a cord to its legs. It should bring out the drive in the pup but I would not do it until it starts to show interest.
You can start training at any age but I suggest you buy a book and/or DVD. Most follow a standard regiment on when to start such and such training.