Social Maturity: An animal behaving within accepted social norms of an adult of that species when interacting with others of his or her species.
I have observed over the years that once dogs reach adulthood, some social behavior changes take place. These are important to consider as you raise and train your own service dog.
As a young pup with the litter and after they go to their new homes, pups are open to everything. He starts to learn basic dog language, and how to inhibit his bite so his playmates will keep playing with him. This early 'window of socialization' of 5 to 12 weeks is what anyone training service dogs takes advantage of. Everything (people, other dogs, other animals, things, locations, events, surfaces, machines, sounds, smells etc) that the dog has a positive exposure to in this period becomes familiar and this stays with the pup to support him through the various fear periods. If the positive exposure is continued periodically until social maturity, the dog will be comfortable with the things he has been exposed to.
Anything that is not experienced positively in that socialization period, becomes something to be suspicious of and without support from the handler may become a source of lifelong fear. Most dogs can be worked through them of course (depending on the genetics, temperament and health of the individual dog), but that puts an extra barrier in the way of success as a service dog.
As the dog pass through adolescence, he learns how to inhibit his bite further in play so he doesn't hurt other dogs or people. He learns what is polite behavior, which dogs would like to play with him and what behavior gets him a correction from another dog. He learns to read the subtle and quick communication of his species. He learns how to respond to the communication to diffuse potential confrontations. And he learns to make choices not to engage at all.
An Example of Changes in Social Maturity
The off leash dog park is a great place to observe this change of social behavior in dogs. (If you are going to use dog parks, I recommend the type without fences and that have trails so that dogs can walk with the handlers and beside other dogs. Face to face contact is minimized as they pass other groups of dogs moving in the opposite direction. High volumes of dogs in small fenced areas with non-attentive humans is a recipe for disaster in my experience.)
Young adolescent dogs go to the dog park and make a variety of dog friends. Typically, dogs chose dogs that have a similar style of play that they do. They run side by side as the group moves along the paths, distracted by things to sniff and look at. As they move through adolescence (whether intact or not), they continue learning how to interact with other dog breeds, ages and energy levels and which ones they like and others they do not like. In this walk structure, things usually don't escalate too much, unless the handlers stop to talk.
Not all interactions are totally positive and some dogs (breeds as a whole and individuals) are more resilient to this than others. The closer they get to social maturity, the less open they are to prolonged interactions with unknown dogs whether the breeds are strange or the individuals are unknown to them, or the dogs are rude or snarky.
After a few unwanted altercations between dogs, the humans will typically decrease how often they allow their dog to stop and greet, how often they go to the dog park or they stop going to the park altogether. So in most dog parks, you typically see dogs that are 3 years old and under. This is especially pronounced in fenced dog parks where the dogs are left to entertain themselves.
When Does Social Maturity Occur?
Typically, by the age of 2-3 years, most dogs have their set of friends they are comfortable with and have most of the communication skills and self control they need to live a generally peaceful life with most other dogs. If they meet adolescent dogs, they are less likely to want to play, decrease the duration of play and are less tolerant of rough play from the adolescents (although "puppy license" is still given to pups under 5 months or so).
The exact age social maturity occurs varies. Some breeds as a whole take longer to reach social maturity (golden retrievers, labrador retrievers, standard poodles), while others are more open lifelong in general (scent hounds as a group tend toward being dog social lifelong as a function of how they were bred to work in groups for humans). In general, I find the smaller dogs are socially mature earlier at 18 months or so and become less tolerant of rude greetings and rough play especially from larger unknown dogs.
What's the Biggest Change Observed?
Once each individual reaches social maturity, they are very happy to see old friends but are less interested in meeting new dogs. Most well-socialized dogs can, however, make new friends, but the process takes longer and multiple meetings are typically needed before the are fully comfortable with other dogs. Then they are included in a circle of friends.
You'll see this with leashed group walks. At first the dog are uneasy when the group first meets.
Who are these new dogs? What interactions are expected of them? Once the walking starts, they have a task to do.
Walking in the same direction as other dogs gives them time to assess the other dogs in a non-confrontational way so when they do meet face to face at a later time, they already have some history with the other dog to draw from. They can smell the other dog's scent in the air, they can watch his body language and see how he responds to subtle communication from himself and other dogs.
This structure mimics a more socially acceptable way for dogs to meet. They approach on an arc at a distance, then circle nose to bum. Joining in on a big circle walk is actually the best way to join a group. Or if the dogs are all sitting, have them face the same way in the large circle (clockwise or counter clockwise). Once the dogs understand the safe social structure of the walks and that the other dog to dog interactions are minimal, everyone settles in to the job they need to do.
(By the way, face to face meetings are considered rude in a dog's world but since most people insist that's how their dogs meet, especially on leash, we do have to teach service dogs to be able to politely do that. At the very least, we can ask them turn and face us so they are not facing the unknown dog or rude dog.)
The decreased interest in other unknown dogs at social maturity is also what makes it easier for them to learn to ignore other dogs when they are working. They may still get excited when meeting their friends, but show less interest for stranger dogs and eventually learn to keep working despite the proximity of other dogs.
What Can Your Do with This Knowledge?
First, observe your dog and other dog's responses. When you first meet a strange dog, does your dog politely turn his head to the side to avoid confrontational direct contact or does he rush right in? If you don't know how to read dog language, check out Turid Rugaas little book that introduces you to 30 common behaviors dogs use to communicate. On Talking Terms with Dogs: Calming Signals. You can't interpret what you can't see!
Find people with dog social dogs to walk with on a semi-regular basis (once or twice a week), on leash or off. This will keep your service dog's social skills polished and decrease his interest in other dogs. It is also great situation to practice and generalize his service skills. Use the environment to practice specific public access skills. Plan places to stop at benches to practice tasks. Find stairs to practice walking down on a loose leash. Ask the other handlers to help train greetings. Practice the Canine Good Citizen (CGC) Test items. Be creative!
Try joining a dog club, ask some neighbors to join you or create FB group to advertise your walks. Explain the basic structure of the walks at the beginning for new members so everyone is clear on the expectations. It's also a great social outing for you! One of my group rules is that they must use positive only equipment and interactions with their dogs.