This does not sound like normal teenage phase stuff to me. But I could be wrong, all dogs have their quirks. Good choice asking for advice! A dog trainer/behaviourist could be a good idea to consult if you have the possibility to do so.
The resource guarding is something you want to get ahead of as soon as possible. I don't know how much you know about training and preventing this type of behaviour, but there is good advice on here concerning how to deal with it. The main thing is to
never challenge them on it. Train and build trust to prevent tense situations.
So if he guards his bed, don't approach him there, train him to come to you instead. He needs to know that his bed is a safe place he can go to when he wants to be left alone. Call him away from the bed and reward him if you need his attention. If he trusts that he is safe in his bed, he will not have a reason to guard it. If you ever need to remove him and he does not come voluntarily, use a leash to guide him rather than direct contact.
Has anything happened to make him feel insecure about his head? Could be someone accidentally hit his head or a child pulled his ear or anything that made him feel unsafe? I would want to rule out pain if my dog suddenly got reactive about being touched. A visit to the vet to make sure there are no issues with his ears or teeth or eyes or neck would be a good start.
Can he see well, have his adult teeth come in correctly, any chance of ear-infection, sore neck etc. The behaviour you describe him showing when you touch his head is him sending very strong signals indicating he is uncomfortable. Question you need the answer to is why? Why is he afraid of having his head stroked.
How you react to him growling is important too. Many people will challenge or punish a dog for growling and escalate the problem rather than getting to the bottom of it. I don't know how you respond when your dog does this, so I'll just throw out a reminder that this is your dog communicating with you, communicating discomfort and giving you a chance to find out why he is not happy in these situations.
Good luck, sounds like he is a great young dog and you are in a good position to avoid this becoming an issue
