I think that's heavily dependent on breed. IMO, there would be no benefit with a small breed, but a later maturing large breed - possibly. I just feel that, because there doesn't seem to be any information I can find that suggests any correlation whatsoever with longevity, I would neuter even earlier in a dog that is not destined to show or breed. The "marking" thing is partly a training issue, more a hormonal one, but why leave a dog intact, only to have to punish his normal canine behavior, which could have been prevented? I don't get that at all. If a dog is just as healthy, does it really matter if he is "filled out?" And, does that even last once he is neutered late? I don't feel my hound has the same tone he did when I adopted him as a 2+ year old intact male.
I would wait longer than 4 months to spay a female, though, because there is some evidence that waiting a bit can prevent spay incontinence.
Regional Director for Massachusetts, International Positive Dog Training Association
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Fergie, Retired Lap Dog, Age 20 1/2
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"If you talk to the animals they will talk with you and you will know each other. If you do not talk to them you will not know them and what you do not know, you will fear. What one fears, one destroys." - Chief Dan George
"The fidelity of a dog is a precious gift demanding no less binding moral responsibilities than the friendship of a human being. The bond with a true dog is as lasting as the ties of this earth can ever be." ~ Konrad Lorenz