I don't know what the earliest age for safe neutering is. I only
know that it is safe at 6 months or older. I believe the veterinarians
reporting that they are having no problems with neutering as young as 8
weeks of age, but I can't support their claims with objective studies.
Personally, if there was a strong need to neuter younger, such as exists
at humane societies, I would have no qualms about it. I wouldn't neuter
my own pet prior to five or six months of age, though.