What made you want to look up low-pressure? Please tell us where you read or heard it (including the quote, if possible).
While spaying is traditionally recommended for kitties between 4 and 6 months of age, spaying as young as 8 weeks old is considered safe, according to Cat Channel. Many animal shelters actually spay kitties prior to adopting them out at this age.
Kittens should be spayed or neutered when they reach sexual maturity, which is usually between four and six months of age. However a cat can be safely spayed or neutered at any age, so even older adopted cats should have this procedure.