i did tobys neutered at 1 year old.
many vets will say at 6 months old.
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I recommend reading the following links pay close attention to the neutering of immature dogs. 6 months and 1 year are immature dogs.
http://www.naiaonline.org/pdfs/LongTermHealthEffectsOfSpayNeuterInDogs.pdf
http://trinitylabstexas.com/what-age-is-best-to-have-my-dog-spayedneutered/