
Hi!
First off, you're right about his age. He's now entering the "Kevin stage" (remember the teenager Harry Enfield played on TV that was always grumpy and moody?) and yes, a lot of Goldens go through it. Keep up with the training.
Secondly, to make life easier, make sure you put as many items as only possible out of his reach. In other words, get rid of temptation whenever possible. I have a 13 month old Golden and I've recently virtually cleared everything off my worktops as she suddenly realised that she could get things down from there. She would even take plates and glasses off the draining board! The good news i,s they DO grow out of it. The bad news is, it can take up to age 2 years.
There is a good article here that deals with resource guarding, which is what you are seeing:
http://ahimsadogtraining.com/blog/resource-guarding/If he growls at you over food, start ADDING bits of food to his bowl whilst he is eating. That way he learns that you being near the food doesn't mean the food will vanish, it means the opposite.
If he pulls a lot on the lead, use a head collar such as a Gentle Leader.It makes things so much easier. He will dislike it at first but dogs do get used to it, and I have found with mine that after a while (even if it is after a year or so sometimes) they stop pulling and can go back to wearing normal collars instead.
Good luck!