We've juvenile spay/neutered 1319 kittens and 417 puppies (2-6 months) over
10 1/2 years of our vet's practice.  Complication % are well below the 6
months+ group.  Reports of additional weight gain or personality changes in
juvenile spay/neuters is also less than with 6 months+ animals, and that was
darn minimal for them.  Your experiences are idiosyncratic, and while I'm
not downplaying what you assess in your own cat, the changes you describe
are not at all common and perhaps are due to the individual personality of
the cat and his interaction with his environment and not directly
attributable to juvenile neutering versus waiting until he was older.  Just
because A follows B does not mean A *causes* B.  Only one out my 6 boys
decided to become a cat balloon after neutering, and it wasn't because of
the operation at all, and he was a year old when it was done.  It was
because he was a stray that didn't know the source of his next meal so
whenever food was provided, he'd eat, whether he was hungry or not.  We're
working on behavioral modification of that tendancy, and at least he's not
gaining any more weight, but like humans, it's a lifelong battle.  None of
the juvenile spayed girls have a weight problem, and none of the rest of the
juvenile neutered boys do either, including the one that was neutered at 6
weeks when he was 1 1/2 lbs.

Sunflower

Sunflower