My girl was just spayed 2 weeks ago, ( she just had her stitches removed on Sunday) she was 6 and a half months old. My vet does not spay or neuter under 6 months. however when i first got her i took her to this different vet for a check up (didn't like them so i switched) and they said they can do it as early as 5 months.
If you wait till 6 months more of her baby teeth can fall out so then the vet bill will be alittle less also cuz less teeth will have to be pulled. (Rylie only had 1 baby tooth pulled.
I guess it all depends on the vets prefference.