I don't have advice, but I can tell you about my experience. I adopted a boxer that had testicular cancer from a retained testicle. It was a sertoli tumor. Because it was a hormone producing tumor, he had feminization. Very large nipples, hair loss on his legs, and some urine leakage. He was six years old when I adopted him. The cancerous testicle was removed and he remained cancer free. Because he was a stray with no medical history, there's no way to know how long he'd had cancer, but I would bet it wasn't five years. While my boy remained cancer free after surgery, he did have issues involving dripping pus from the penis that we were never able to resolve before his death. He wore a belly band 24/7 which meant he always had UTIs. The pus was likely a prostatic issue rather than being directly related to the testicular cancer. I would probably not neuter just yet. I would discuss the chances of the testicle becoming cancerous in the next year and see what the vet says. I would think that would be something you could monitor. In your position, I would have him neutered at 18 months. Sooner if there's any indication that there may be a problem. There's no sense taking a chance. From an aesthetic rather than a health view, Leo's nipples really detracted from an otherwise gorgeous dog. We didn't love him less. I even forgot he had big nipples, but I was reminded every time someone asked why "she" had a penis. Lol. Poor Leo.