I've early neutered for about 4 years now. At first, only one vets in our practice would do it - but after the others saw how easy it was, and how quickly the kittens recovered, they're all converts. They also agree that size is important, and prefer the kittens to be around the 3.5lb mark as an absolute minimum. The weight is important due to heat loss during surgery. Many vets will early neuter boys, but not girls.