I had a 13 year old Saddlebred stallion gelded after he had been thrown out on a 30 acre property with a handful of mares to run wild. He was downright dangerous as a stallion and would go after anyone who tried to get to HIS mares. The vet came right out and said she didn't know if it would make a difference but... luckily, it did. He became a wonderful gentle gelding that almost anyone could ride.
The way I looked at it was... it wasn't going to make him worse so it was well worth the try. Thankfully it paid off big time.