Some vets will say early, some will say later. My vet told me if you do it too late though you lose several health advantages due to hormones already having been released. But give your vet a call, they'll have a better answer than any of us.
I would not trust your vet. Many push for early spay and neuter despite the new research. Do some research on your own.
The health benefits of waiting outway the benefits from doing it early. So much so that many breeders will nullify their health guarantee if done before 18 months old.