newfoundland puppy

Question
Hi,
I just purchased my 4 month old puppy from the humane society, a Newfoundland mix (I think with lab)! He is wonderful, gets along with the kitten my roommate has and other people perfectly. However, I took him to my friends house to visit with her dog (hoping I could find him a playmate for while I was at work). I don't know if he was reacting to the energy and uncontrollability of my friends lab or if he is just uncomfortable around other dogs but he started barking and growling and snapping at the lab. He is completely indifferent to other dogs unless they start to approach me or him and then he starts this low gurgling growl. I had a bad experience years ago with my Shepard and Terrier tearing each other apart so when dogs start showing aggression to each other I panic. I try not to show it, and in no way do I fear for myself, but I know the dog senses this. His tail was always wagging, but the vocal and body language do not say 'let's play!' Or at least that is not what is perceived.
I know I need to rectify this problem before he gets any bigger and I cannot control him, just from his shear size. I am beginning training classes shortly. However, I am apprehensive because there will be other puppies in this class and I don't know what to expect. He will be a little older then the majority of puppies in the class and already seems to have aggression toward other dogs.
I guess my question is, Do you have any advise (more for training me to handle him then training him)? Does wagging the tail mean play or should I pay more attention to the growling and sound? Is there a general cut off age that it is hopeless to think that your dog might socialize well with other canines?
I have been around dogs, horses, cats...all my life but this is MY first dog. The first time I am the one training and taking care of him by myself. I want to make sure that I give him the care and life that he deserves.
Thank you for your time!


Answer
Sounds more like rough play,rather then actual fighting

It depends on the type of tail wag the dog has-a stiff wag that is upright is dominance,while a tail wagging fast and at mid height,is playful,a fast wag between the legs is submission,and while a low slow wagging tail is content

Now what you can do,it have both dogs play with other while both muzzled at first,so that they can't hurt each other,until they get used to each other,then they can come off