Jassy,your little Gizmo is just doing what kittens do,I would not call it aggression ,just try to avoid playing with him with your hands.
As for neutering,my vet at the time would not neuter before 6 months,but I know some will do it much earlier,all 3 of my boys were neutered at 6 months
We did have a spraying problem,I am not sure if it was related to being neutered later.
"The cruelest animal is the Human animal"
3 kitties,Rocky(r.i.p my boy),Chico,Vinnie