Size of a four month old

Question
Hi,
I have a four month old male aussie shepherd and recently took him to the vets to get his four month shots. When I was there the vet made the comment that he was rather small for his age, however, she did say that she had very limited interaction with the breed. He is 11kgs and pretty active. I was wondering if you know what are the rough guidelines for size of an Aussie shepherd and whether I should consider having him neutered after 6 months to allow him to grow a little bigger. This was not advice from the vet but was suggested to me by other dog owners. He is exceptionally well socialised with other dogs and people and I am not greatly concerned with him marking his territory as we live on a large property. It would be great to hear you input.

Thanks,
Jack

Answer
There is no strict size standard for Aussies because the prime reason for breeding them was so that they could work cattle.  Tenacity and smarts were important, size not so much.  My female, at age 4, is barely 19" and weighs only 36 pounds.  Her dad was 40 pounds, mom 32.  She is from working lines, and they tend to be smaller than the heavily boned show dogs you sometimes see now.  11kg is 24 pounds if that helps your vet to determine how well he thinks your particular dog is developing.