Most will have different view from me. I think it's good to leave them till there about 9 to 10 months before you start them. Gives them time to mature a bit in the head and body. I've started them earlier and most people will, but i don't think it hurts to give them a bit of extra time. I'm happy to take them out earlier to get use to the bush.
Best to start a young dog with an experienced dog. Monkey see, monkey do. Be patient, and don't try and force the dog to go at a faster pace than it can handle.