
If your puppy is six months old, you have likely watched him go through his fast-growing juvenile stage from age three to six months. Now that your puppy has reached six months of age, he can be considered an adolescent.
During this time, your puppy's physical changes will slow down a bit. Energy levels may increase and you may see a newer side of your puppy's personality. Be prepared to adapt to your puppy's needs in this life stage.
Physical Development
By six months of age, your puppy's growth will slow down. Most small dog breeds will be nearly finished growing at this time, though they may continue to fill out over the next three to six months. Medium dogs often keep growing for a few more months, but at a slower rate. Large and giant dog breeds tend to keep growing until they are 12 to 24 months old. Between six and eight months, many puppies have a lanky and awkward look that is quite adorable.
Most dogs are house trained and in full control of their bladders and bowels by the age of six months. House training is mainly complete at this point. Some puppies will still have an occasional accident in the house, especially if there is a change in the routine. Continue to be patient and consistent; this is normal. If your dog is still having major issues with house training, contact your vet for advice. Your puppy may have a health issue that can be treated.

Your puppy should have all of his adult teeth by six months of age. This means that teething is over and your dog may chew less obsessively. Remember that it is still normal for dogs to chew, so make sure you have healthy dog chews available.
Dogs reach sexual maturity between six and eight months of age. Many pet owners choose to have their dogs spayed or neutered by six months of age unless they are quality purebred dogs being bred by a responsible breeder.
If you have not neutered your male dog, he will begin to show an interest in female dogs, specifically those in heat. He will go to great lengths to mate at this point. Whether neutered or not, he will likely begin to lift his leg to urinate (if he hasn't already) and may begin marking areas with urine. Marking behavior can be curbed more easily if you stop it early. Catch your dog in the act and redirect him to an appropriate place. Marking behavior tends to be less severe in neutered dogs.
If your female dog has not been spayed, she will likely go into heat (estrus) between the ages of six and eight months. She can easily become pregnant at this time if she is with a male dog. She may also try to escape the house to mate.

Behavior Changes
Your six-month-old puppy is an adolescent now, and his behavior may show it. He may have an increase in energy and willfulness. The dynamic between other dogs may also change; adult dogs can now tell he is old enough to know better and will not go as easy on him if he steps out of line.
Just because your puppy is past the optimum socialization window, it doesn't mean that socialization should stop. Your puppy is still exploring his environment and learning new things. Continue to expose your puppy to new experiences, people, places, things, and sounds. Reward for calm behavior and ignore fearful behavior.
It is common for adolescent puppies to exhibit some destructive behavior in this stage. This is often caused by boredom due to the increase in energy and confidence. Continue to provide plenty of exercise for your puppy.
Puppies between six and 12 months of age may sometimes act like they forgot their training. Be consistent and firm. Continue to have regular training sessions, covering the old basics again, and mixing in newer, more difficult tasks.

Health and Care
Now that puppy vaccines are completed, your puppy will not need to see the veterinarian until adulthood (unless something is wrong). Be sure to watch your puppy for any signs of illness. Contact your vet with any concerns. You are still learning what is normal for your puppy. It is much easier to treat most health issues if they are caught early.

Food and Nutrition
Proper nutrition is an important part of your puppy's development. In general, you should continue feeding puppy food (dog food labeled for growth) until your puppy is done growing. Large breed dogs often need to stay on puppy food past their first year, but other dogs can usually start to transition to adult food between nine and 12 months of age. Small breed dogs may even transition earlier.
Because your dog's rate of growth is slowing at this time, it can be easy to accidentally overfeed. Make sure your dog's growth is overall, not just in his belly. Obesity in dogs is a rapidly growing problem in this day and age. Ask your vet for advice about your dog's optimum weight. Your vet can also tell you when to transition your dog to adult food.
When feeding treats, make sure they are non-toxic, healthy, and not fed in excess. Dog treats should never make up more than 10% of your puppy's daily food intake.
Warning
When giving chew treats, avoid bones, antlers, hooves, hard nylon dog toys, or other hard chews. Even though the adult teeth are all in, they can easily be damaged by chews that are too hard.
Training
You are never truly done training your puppy. Even adult dogs need regular training to keep them sharp. By this time, house training should be basically complete. Now is a good time to fine-tune obedience training. Continue to practice basic commands like sit, stay, and down. Add more advanced things, like roll over. Keep working on the recall cue and add in an emergency recall



As your puppy matures, you may notice new behavior problems cropping up. Address them as soon as possible. Don't assume your puppy will grow out of it. The longer you allow inappropriate behavior, the more difficult it will be to correct it. If the issues are too hard to manage on your own, seek assistance from a dog trainer or behaviorist.
Guide for Introducing an Older Dog to Accept a New Puppy