Our latest pup was neutered right before we got him they guesstimate at about 12weeks. He was rambunctious and his stitches opened slightly but he healed just fine. I just wrote a research paper for school on spaying/neutering and from what I found in a few different articles it is best to spay before the first heat cycle and neuter before 6months. Neutering before 6months eliminates the possibility of testicular cancer. The AMVA (I have sense some people on here arent fans of them I'm just stating what i've found it was also backed by Canadian Veterinary Medical Association, British Small Animal Veterinary Association and the American Animal Hospital Association ) suggests pediatric spay and neuter are the best. Pre-pubescent procedures are quicker then adult dogs therefore less time under anesthesia and less complications. They also say younger dogs heal better then adults. The procedure is being done as young as 6weeks now.
