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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 may be spayed as early as 8 weeks of age, up to 16 weeks. After that, the kitten is pretty much an adolescent cat. Spaying formerly was recommended after the age of 6 months, when the female cat reached sexual and reproductive maturity. Cat overpopulation is a serious issue, and feline euthanasia rates are high at many animal shelters. Thus many shelters now require spay/neutering of kittens before adoption.