Shoot most places neuter before 4 months in my state, it's the law for rescues and shelters they can't adopt out an intact animal over 4 months. If youre worried ask your vet about a vasectomy which keeps 100% testosterone or a zinc neuter which is still about 60% testosterone left.
I neutered my boy at 2 years. I would wait but legally some places you just get it done and if that's the case I would so it ASAP to be I compliant with the law
Take a look at the Heath section I posted a few spay neutering studies over there a fee months ago.
If you can't contain your dog with 100% certainty get it done.