Good advice so far. I would add that the age is not as important as the person holding the transmitter. Some programs start as young as 4 months, most others about 6+. My advice, don't turn it on until you have checked out a program that lines out how to use it.
I agree. With my pups I start at 4+/- months. If you've never collar conditioned a dog then get Bill Hillman's puppy video or work with a pro.