Generally anything the ASPCA has to say should be taken with a grain of salt.
I would listen to your breeder if nothing else it may void the guarantee for health if you have it done too soon as early spaying/neutering has come to light to cause a lot of problems in dogs. I have a video a vet did on a study of early spay/neuter. Its rather lengthy as its around 30 min long. But eye opening non the less..
Certainly the ASPCA is not unbiased and will heavily favor neutering, but the info in the link actually seemed decent to me.
I did lose a very nice sheltie in 2001 to prostate cancer, however, and the info from the vet at the time was that not having him neutered early probably led to it. It would be good to get more modern info. It makes sense, that at least for some of the adenocarcinomas, that testosterone would accelerate the tumor growth.
Last edited: