The key is how fast the dog is learning. As long as he grasps and accepts everything without showing stress, keep advancing. Odds are a spring pup brought along at his own pace will be ready to hunt on opening day. In fact, if you followed a good book and didn't procrastinate, your youngster will be better trained than most retrievers you'll see in the field. Between 8 and 12 months, dominant-type dogs experience strong urges to be the alpha wolf.
Obedience becomes more strict.
Add stronger behavioral moves to show your dominance. And let him make mistakes with consequences that demonstrate that he should have listened to your advice. Unless you're satisfied with his field ability, training will continue. Doubles and triples. Two or three days a week for 15 to 30 minutes a day is enough to maintain obedience and add refinements.