I wasn't going to reply to this thread, my view differs from many on MN, but as Solo2 has asked some very valid questions, I will do.
I would never neuter any dog unless there was a specific reason to do so and I would never neuter a dog that wasn't fully grown, so for most large breeds, 2 years plus. That's not to say I think that should apply to all owners, particularly for bitches there are many more reasons for neutering than for male dogs and so the situation is not as clear cut.
Solo2, I think what your breeder may have been referring to was early neutering. There is quite a bit of evidence to show it slows the closure of the growth plates, leading to taller, leggier dogs (this has certainly been well documented in horses for a long time now) which in turn can exacerbate existing or underlying joint or hip problems. I have also seen some very odd looking dogs (especially males) that were neutered early. There is also some evidence to suggest that neutering too early increases the risks of some cancers, such as bone cancers and can cause incontinence problems, especially in bitches.
Keeping an entire dog does not mean you have to or want to breed. I have four currently un-nuetered dogs here. Yes, I am a 'breeder', but my dogs are my pets first and foremost and their welfare is paramount to me. At least two of those dogs will never be used for breeding, probably three. I also manage (easily) keep an entire male in the house, under control at all times, even when the girls are in season, and will not be having any 'accidental' litters. He will be neutered though, as it will make mine and his life better and easier (he does know when the girls are in season) but we have waited until he is mature. Otherwise, I would be leaving him entire.
When we have had puppies I leave the decision to neuter up to the new owner, but I do ask they discuss the pros and cons fully with their vet (I do find vets are often quick to discuss the pros only, as Kid very, very sadly found out) and make their decision based on all the evidence. I also personally prefer them to wait until at least after a bitch's first season to spay, for the reasons mentioned above, but the decision is ultimately theirs and I am an experienced dog owner, not a vet.