Maybe your vet is right, I'm not sure about the research on dogs, maybe there aren't any good studies of the effects of castration on the skeleton. But, there is no doubt that testosterone (and "female" hormones - oestrogen) regulate bone growth - so removing these hormones while the bones are still growing is likely to have some sort of effect on the skeleton - even if there isn't much evidence for exactly what the effect is. I have a friend who's a vet in the UK, and she can't believe that I haven't neutered my boy! Her main reason is to prevent unwanted litters - and she would advise all owners to neuter once their dogs are fully grown, if they don't want to breed from them. She sees lots of irresponsible owners who come in with pregnant bitches - so I can understand her perspective. I'm in Germany too and know a lot of neutered dogs where there were no health reasons. It's not illegal here - but I think it is in Norway. The German animal welfare legislation prevents any unnecessary surgery, but there is a section for sterilisation in Article 6 here: https://www.animallaw.info/statute/germany-cruelty-german-animal-welfare-act For example, all of the shelter dogs here are neutered, and I think about half of the dogs I know are neutered - some because they came from a shelter.
Charlie is a rescue dog and was neutered at around 6 - 8 months of age. He came to live with us at 9 months, he was tall then, he is a Labrador x Pointer is 6 years old and measures 27" at the withers so a big lad. Maybe his early neutering affected his growth. I think all rescue dogs are neutered and spayed in the UK before they are rehomed.
Research has been done. This one compares Labradors and Golden results for early neutering. For example for joint problems and hyp dysplasya there's an increase of 10 % in labs and 20 or more for on golden. There is also increase on cancers for goldens and non mensurable for labs. But the test is not very broad as it only looks at 3 ttpes of cancer and joint and hyp disp. I trylly believe other issues could arrise. The test also didn't show any benefit for spaying females in regard of mammal cancer... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4096726/ There are a lot more stuff about this, and the labrador site also talks about it. To me is not natural to any being have an important gland removed, remember both gonades (male or female) produce important hormones that are specially needed in the growth period. I made a decision that at least for this time i would not neuter Wuki. As time goes by, he is getting calmer and learning his limits. So... If i can manage not to do it, i wont, specially knowing about this risks.