In my opinion he is a nice size to be neutered
I think the op is a little more complicated if the testicles havent dropped,but im not sure because I dont have males.At 4months old I doubt they will be able to take out all of those baby teeth though because he is too young yet,which means he may have to have them out later on if you neuter him now (unless of course they fall out on thir own
)
Im sure he will be fine