Neutering is where the dogs testicles are removed. When done early, studies have proven many unwanted health issues, ACL and PCL tears, cancer and shortened life among them. However, a dog that has retained a testicle in his body (or both!) needs to have those removed. I recommend neutering only for medical reasons. Your older dog should be examined regularly for changes, lumps, or swelling of his testicles, which could indicate a health issue. Also, older dogs with prostate problems benefit from neutering.