There is a useful study on the Internet entitled “Early-age neutering of dogs and cats in the United States (a review)” 1which answers the question in the title.
Early-stage neutering has increased in popularity. Kittens can be neutered as early as seven weeks of age before adoption at shelters. Studies are evaluating the long-term effects on behavior and health. Early-stage neutering is done to control the unwanted cat population and it has beneficial effects on behavior.
The abstract (summary) of the study states in clear terms, and I will quote verbatim:
“Early-age neutering does not stunt growth in dogs and cats (a once-held belief), but may alter metabolic rates in cats.”
The study was conducted by three scientists: Olson, Kustritz and Johnston.
Dr Bruce Fogle, in his book The Encyclopaedia of the Cat, states on page 56: “Curiously, sex hormones inhibit activity: cats neutered very early tend to grow slightly longer leg bones”.
He indicates, therefore, that neutered cats have longer legs. This is supported by the authors of the well-known book Cat Owner’s Home Veterinary Handbook at page 428 where they state that early-age neutering results in a “slightly taller size due to delayed bone growth plate closure and the inability to extrude the penis”.
Incidentally, if an older cat is neutered after he has mated he may retain his sex drive but it is uncommon. Neutering does not change the male cat’s personality they say but it does reduce his desire to roam and his sexual impulses which as a consequence reduces aggressive behavior. He becomes more affectionate.
1. Published on the ncbi.nlm.nih.gov website.