Reggo, have you been to any obedience classes yet? Some dogs just "get" the walk without much effort (generally dogs with lower drive and energy), but for most dogs, walking alongside the human at the human's (slow) pace is not at all natural and must be trained and proofed before you get a satisfactory result. He may mellow out as he gets older, but he may get worse without any intervention.
Nikon was very, very "dog reactive" (meaning he would bark, whine, howl, growl, and lunge at strange dogs) from about age 4mos - 10mos. During that time, I did a lot of work building our bond and communication so that the was more focused on me, and also a lot of training. I train dogs for competition but my dogs also need "regular" obedience training like walking calmly on a leash, obeying me when we are away from home, ignoring other dogs, etc. The more I trained Nikon how to behave in public, the less he cared about other dogs. Now we can pass strange dogs on the street and the most he will do is raise his hackles a bit but he passes by without any lunging or noise. Yesterday we started a new obedience class and he laid down next to a Basset Hound he's never seen before. Ironically the Basset owner said her dog is scared of other dogs and my dog used to want to attack other dogs, but they were lying with their heads down about 4 feet apart.
So anyway, some of the dog reactivity could be a phase, but if you don't intervene and move ahead with training the dog can get stuck in that phase or develop self-rewarding behaviors that make it worse. Most dogs get reactive at another dog out of fear/uncertainty. They think "OK if I make myself look really mean first, the other dog will just leave and I won't have to deal with my uncertainty." So say you walk past a dog and your dog is pulling, barking, carrying on and he continues to do this as the other dog passes and walks farther away. The dog has just been rewarded for his bad behavior which is what you don't want.
The first thing to do is always setup the dog for success. Do not give the dog the option of reacting to the other dog. If you see another dog coming, immediately turn your dog around and go the other way. Once the carrying on starts, it's almost impossible to correctly redirect the dog. We tighten the lead and hold onto the dog to maintain physical control but the tension is passing to the dog and the physical touch from the owner is actually interpreted as praise. If I didn't see the other dog soon enough and Nikon started a fit, I turned around and walked the other way, totally ignoring his fit even if I had to drag him away, and when we were far enough away for him to calm down on his own, then I sat down, pet him, and praised him for being calm and stopping the fit.
Anyway, as for the walking training bit, the best suggestion is to get with a good trainer. It's not so much to learn the method, but learn the psychology behind the method, and how to communicate with the dog. There are also a number of tools out there for "puller" dogs. I have a prong collar, a Gentle Leader head halter, and an Easy Walk no-pull harness. I would try the Easy Walk if your dog is reactive to other dogs. Reason being that with a prong or head halter, if the dog lunges for another dog, they will get "corrected" by the prong links or the halter being over the muzzle and might associated the negative feeling with the presence of the other dog, only making the problem of being uncomfortable around other dogs even worse. The Easy Walk harness is a front clip harness, so it won't injure the dog's head if he lunges hard, or pinch the neck like a prong collar. These are all good devices for gaining initial control of the dog, but the key is the real training that happens so that you don't need these as a crutch forever. I would also take some food or treats along and just randomly give the dog a treat from your hand anytime his head is near your left pocket (or whichever side you want him to heel on). If he's food motivated he will find out soon enough that pulling and going ahead to sniff = no treats and staying on pace with you = treats. Another thing people do is "make like a tree" and/or "penalty yards". Make like a tree is just that, if your dog pulls and ignores you, you stop and plant your feet. You *only* move forward when the dog is NOT pulling at you. At first this is very frustrating for you and the dog and it's not uncommon for someone to move half a block in over an hour, but the dog needs to learn that pulling is simply not acceptable. The penalty yards means that not only do you stop moving if the dog pulls, but you walk backwards and the dog has to move back and start over again at your side before going forward.
There's really dozens of good methods, but different ones work on different dogs. It's a matter of trying and being really patient and consistent.
