When Does a Puppy Reach Maturity?

It's hard to look at your little puppy and think of her having a litter of her own, but it can happen sooner than you'd expect. Generally speaking, dogs become sexually mature as young as 6 months of age, regardless of their breed or gender. This change can cause personality changes as the various hormones start surging, such as increased friendliness and affection in females, and more aggressive behavior in males. Territory marking may start, causing your little puppy boy to raise his leg and leave his scent around the house. The urge to mate could override your little lady's otherwise good obedience, causing her to roam and find herself a boyfriend.

Once the initial hormonal surges of sexual maturity start to even out, your dog's emotional state begins to stabilize. Before this, your pup could behave like a small, furry teenager -- acting out, testing boundaries and generally making a nuisance of himself. Somewhere between one year and 18 months of age, your pooch will settle into his personality and find his place in your pack. Smaller breeds tend to mature nearer the one year mark, while larger breeds fall more on the 18 month end. All dogs are different, however, and mature at their own rate, meaning your little shih tzu may take up to two years to outgrow the puppy behaviors.

One of the frustrations with dogs is they can mature physically before they do emotionally, meaning you could have an 80-pound pooch racing through the house thinking he's still a puppy. Physical maturity refers to when your pooch reaches his adult height, which varies by breed. In general, smaller breeds up to 30 pounds are typically full-grown between 10 and 12 months of age, while medium-sized breeds up to 80 pounds take one year to 16 months. Large breeds over 80 pounds can continue to grow until they're 2 years old.

Although it's easy to let that adorable little puppy do whatever he pleases just because he's so darn cute doing it, the key to good behavior in an older dog is instilling it while he's young. Start teaching proper behavior the day you bring your pooch home, and never let something go “just this once.” Consistency creates good manners. Have your pup spayed or neutered as soon as possible, which varies depending on your vet's preferences. Early sterilization can eliminate the bad behavior associated with the hormonal changes when your pooch goes through puppy puberty. Start swapping your puppy's food to an adult formula as he approaches his adult size, and consult with your vet for the proper time based on your individual dog's growth. Your pup will test his limits as he gets bigger, so make sure you assert yourself as the confident alpha in the pack.