Your vet needs to come up to speed on research.
Don’t know what breed you are talking about (it does make a difference), but for many large breed dogs, ou are best advised to wait until the growth plates close.
For large/giant breeds, two years is generally recommended.
If ever…why do you want to castrate your dog?
That is, if you are able to supervise your male so he does not ever have an oops breeding…which is not that hard to do, for some of us.
I have owned many intact male wolfhounds over 45 years, none have ever sired an unplanned litter, none have ever urinated in the house, or displayed aggression to other dogs. They cannot “roam” as we are securely fenced.
None have ever had a medical issue linked to being intact.
I show in conformation, obedience, and tracking (not titled yet in tracking).
Why not listen to your breeder?