There have been 3 major studies on spay/neuter. They are the Rottweiler study, the Golden Retriever study, and the Vizsla study.
While each has its own emphasis they all show beyond a doubt how injurious the practice of neutering males is to their health, especially when done early. It is very damaging practice. Cancer rates go up, hip dysplasia rates go up, obesity goes up, fear/anxiety and issues like noise anxiety go up, confidence and well-being go down and stamina is reduced.
CCL (ligament tears), which often happen in pairs and cost $3000 to $6000 per side to repair surgically are now at such epidemic levels in neutered dogs that at many dog parks "who is your CCL surgeon?" discussions are similar to the "who is your kid's orthodontist?" parents might have.
Routine castration as a means of birth control is something we will be ashamed of as a society one day. It is a very bad practice for the health of individual dogs and the so-called "animal right's" militants are wrong.
Read the studies. They are clear, and quite damning of the practice. Your holistic vet is spot-on (he or she is a rarity in the field these days). If you want to sterilize there are some (but far too few) vets trained to do vasectomies (which spare the hormones and preserve health).
Some males begin to develop enlarged prostates in later age. These can be detected by vets. If the prostate risks interrupting urine flow then neutering at that point is warranted. Dog prostate enlargement is testosterone dependent, and will almost immediately shrink post-castration. The only cancer eliminated by neutering is the very rare testicular cancer (as what's removed can't become cancerous) but it would be crazy to put a dog through the medical risks to eliminate a very rare cancer.
Read the studies. You won't want to do it when you have the evidence. You may become damn angry at the prevailing wisdom, and the damage done by PETA, the US Humane Society, and Bob Barker in promoting the most radical and health damaging options to the pet over-population problem.