Doubtful. An ethical breeder would know that same sex aggression cannot be "taught" or "trained" out of a dog. The age, size, breed, or temperament of the other dog in the equation matters not, nor does what age they are introduced.
Of course not every Doberman on the planet is same sex aggressive, but it is a tendency in the breed. Should you choose to role the dice and keep 2 males you will need to be prepared that it is a possibility you will need to keep them separate for the remainder of their lives. Typically people find that they get along fine as puppies / young dogs, but once maturity hits all bets are off. It's not a training issue, it's something that is just hard-wired into their DNA.
Just like people, dogs have PERSONALITIES. My very best friend is a 30 year Lic Vet Tech and Breeds Dobes with me. She is her clinics behaviorist & Nationalist. She is MY Guru!
We just had this discussion a week+ ago ,about two males in a house, she said she believes two males(IF Neutered) will often get along better than a boy and a girl and particularly a girl and a girl.
While We(Breeders of INTACT male Dobermans would NEVER put to intact males together....it is because they are territorial...and you add in girlie smells etc. to the mix and you get males that are “aggressive” male to male)
When you have a non dominant Neutered male (that has grown up playing well with others,it changes the dynamics quite a bit). And if they get a non dominant “lil brother” that is raised ‘subordinate’ to them, and that ‘brother’ is neutered before he (frankly)turns into an A-whole..The World is At Peace!!.
AND YOU have to be the Pack Leader and be THEIR Leader.....They will take your lead.
I have met plenty of friendly goofy Fun Loving neutered males that get along, and play well, with other males......So while I don’t think your Dobie forums are necessarily wrong..I think they are also operating under the age old belief at you cant put two males together AT ALL....Yet we see it all the time at dog parks and I know of people that have two neutered male Dobermans.
I think the KEY would be to have Breeder knowledgeable enuf to pick the RIGHT pup for the situation.
That is what the breeders response was.