Seems like all labs behave same even my lab did exactly same at 5-6 months old like growling if i take something from his mouth, I think what you did is right, scold him, warn him and even you growl against him when he growl at you. Remember that you are dealing with animal not human baby (I say this as I saw some treat dogs as humans which actually dogs doesnt like that). You should always be top of him in ranking and he should be least rank in your family. Give him food only after all family members had food. Some says this behaviour can be change by positive reinforcement and this rarely works in my case. Understand while raising dogs keep discipline as first and exercise as second then after only comes affection. Teach him disciple, set rules, be calm and assertive, dont allow him to own house or things, you need to own/rule. While going for walking dont allow him to go first, make him to sit and you go first and thenafter take him to follow you. Also when you or some of your family members enters your house, dont talk/pet your dog, talk to all members in your family and finally pet the dog. These things will make your lab to understand that you are pack leader and to obey you.