Stunted growth ???

There is no simple answer on when you should spay or neuter, lots of different advice out there. I think that the main issue isn’t stunted growth but bone development. If a dog is fixed before physical/sexual maturity some hormones that signal to stop bone growth are missed, they can continue to very slowly grow which can cause the density and length of the bone to change. Large breed dogs have more weight baring bones and relay on them more, so it’s more of a concern. Don’t know as much about the smaller breeds. I'd let the dog mature first.