neutering age

Question
I am getting a 4 month old Australian Shepherd from a very reputable breeder. I am planning on having him neutered. I had read that males should be neutered by age 6 months, or around that time.  The breeder has it in her contract that I will have him neutered between 9-12 months. When I asked why so late, she explained, but I didn't quite get it. Something about the dog wouldn't be the same size as the parent?? I will, of course, do what she asks, but could you shed any light on the correct age to neuter? Thank you

Answer
I would not get a dog from someone who restricts my ability to neuter when I need to.  While it is true that dogs may not reach the size of a parent if they are neutered early, it is also true that a dog that will not be shown does not need to be intact.  Your breeder may be trying to hedge her bets and talk you into showing him, or breeding him, later if he turns out to be nice looking as an adult.  The second good reason for neutering earlier is that your dog may not get into the habit of marking his territory with urine, and he may not become aggressive with other male dogs, neutered or otherwise.  I suggest you speak to your veterinarian as well about the benefits of neutering your male dog before he gets to leg lifting on everything.  Neutering after that behavior begins does not always stop the behavior.
Most reputable breeders selling pet dogs, whether they might have been show or working quality or not, require spay/neuter in the contract, and I have known many who require it by age six months, so this is entirely your own breeder's preference, and my opinion is that you do take a risk neutering later.  Not only the unwanted litter if your dog should get loose, even accidentally, but the question of unwanted behavior in a pet dog.  Also, an Aussie who is already four months old is past the optimal age for socialization, so if the dog is not already well socialized, and friendly with strange people and dogs, he likely will never be.  Just a cautionary note in case you thought that remedial socialization was a possibility - in this breed it probably isn't.

You can test the pup to see how social he currently is.  Take him to a strange location and see if he willingly interacts with people, hangs back, or looks fearful or stand-offish.  If he seems ok, and you do take him, be sure you continue his socialization all the way through adulthood - play groups, training, doggy events, etc.