There is so much more to breeding than knowing what age to begin. No one is being hateful. They are just pointing out that if you don't understand something as simple as colour genetics in the breed where colour genetics are simple and readily accessible, you are not ready to be breeding.
To answer your question about age, some of the health tests recommended for Dobermans can not be done until the dog turns 2. For that reason, many responsible Doberman breeders do not breed dogs until after that time and after the appropriate tests are done. And then there are a number of Doberman breeders that do not breed their dogs until they are 4 or so because this is a breed that has a number of problems that take dogs early (like dilated cardiomyopathy and cancer, not that they can't strike at a late onset as well) and they prefer to give the dogs a little more time for a problem to occur and remove them from the gene pool as necessary. Additionally, I find that many Dobermans are not mentally fully mature until 3 or 4 years of age and males often do not fully mature physically until 3 or so. If you want to be relatively sure of what you're capable of producing, it would be a good idea to wait until the dogs you're breeding are fully mature - physically and mentally.
It is a breed where there should be no hurry to breed if you intend to breed well.
The good news is that it certainly gives one a lot of time to qualify their breeding plans through conformation evaluations, health evaluations, temperament evaluations and pedigree research.