Caponizing usually decreases aggressiveness--obviously this won't help in an older roo with the HABIT of aggressive learned behavior.
It does not stop crowing, although it does decrease it.
I caponized a pet silkie with the help of a local vet, who provided isoflurane gas anesthetic. I'm sure once you are talented at this surgery, you can do it without anesthetic--they have been known to eat DURING the operation. The incisions are small.
Some books describe taking both testicles out via one incision; this is risky, as it increases massive bleeding potential by accidental tearing of an artery.
The skin is pulled taut (upwards) before the incision is made through both skin and muscle; that way the skin incision, when released, ends up in a different location--lower than the muscle incision. This essentially creates a one-way flap-valve which can "burp" air OUT of the abdominal cavity after surgery, while not allowing air from the outside to enter. We did put a stitch in the muscle to reapproximate the ribs, but farmers did not. Caponizing was WIDELY practiced in the past--the 40's, maybe???
We had a lovely arsenal of surgical equipment to choose from, and it was still devilishly frustrating. The testicular tissue is very friable--falls apart when grabbed, even worse than your cut piece of calves liver. You must get both testicles completely out, or he will be a "slip"--still a rooster.
I would want MUCH more practice before doing this without anesthesia, so that it could be done quickly.
Age: I did mine older than 6 weeks--my guys were crowing for a couple of weeks. He did GREAT--no apparent discomfort. I kept him cooped for a day or two after the surgery, just to reassure myself! He acted perfectly normal, and foraged happily when I let him out.
It's difficult to see in there through small incisions (excellent moveable lighting is essential), and difficult to spread those tiny ribs to get a work-space. The testicles are deep in the cavity. (A fryer chicken from the grocery will show you the testicle and it's placement.) Worst of ALL was trying to grab those little buggers!!!! I finally grabbed a few (clean but unsterile) long-handled "Q"-tips (cotton-tipped applicators) and scooped them out with those! (They were already detached by then.) That worked well--they kept slipping off the instruments when we tried to pick them up, but they stuck to the dry cotton.
Regarding vets: Good luck finding a vet to caponize. I live in Ohio--we are a farm state--and I couldn't even find a vet (numerous long-distance calls to rural area vets) to get advice about my first chicken--a stray with a severe respiratory infection! I ended up buying over-the-counter parrot meds! If you can find a vet who does it, it's likely to be expensive. The vet who helped me did it out of curiosity, and I provided all the instructions and diagrams, and we did it together, after I reassured him that I understood that: 1. It may not work. 2. The bird might not survive. 3. I would be sad, but I can take it. He had handled chickens back in his school days (research project using chickens), so he felt comfortable with them, and he was curious. I doubt he would bother with it again. Your vet cannot provide anesthesia and let you go about it yourself; he would risk public censure and veterinary board action.
I'd do it again--the caponized roo became more docile. His non-caponized "sibling" continued to become more territorial, as is normal. Non-aggressive roos are more fun, and safer around children. He was a healthy bird for the rest of his life.
If you can find someone EXPERIENCED in caponizing, enlist their aid. Farmers with generational farms might have retained the skill, and if you have Amish in your area (if they are friendly to "English") they may help you--$10. may get you a caponized bird. I'd provide the sterilized, or at least boiled and clean) instruments--the Amish don't put much money into individual chickens. They may well think you're joking about paying them to do this, and undoubtedly won't want your potentially diseased bird on their property. (Not mean--just good animal husbandry through disease prevention.)
If you get a vet to assist you, I would recommend a gallbladder stone forcep for the job of grabbing, twisting and pulling (twist and pull is safer than cutting!!!!), as well as the afore-mentioned long-handled q-tips! As with anything else, you can probably find one on e-bay, searching "surgical instruments."
If I lived in an area where the neighbors would accept some crowing, I'd do this to keep my pets. As it is, I'm in the city; unless I can learn to "de-crow" a rooster, I'm stuck. I had pre-arranged pet homes for in case my chicks became roosters (they both did), but finding what I consider good homes for roosters is next to impossible, and I get too attached to dump them in a sub-optimal situation.
To those that suggest de-crowing and caponizing is cruel--a reminder that a lovely long, spoiled life is better than a hatchet-job is in order.
And no, I do not eat chicken.
There is a vet who will discuss "de-crowing" roosters (he describes it as simple) with other VETS--Ross E. Babcock, DVM (609) 944-9661. I was advised by a hatchery that this is "very high risk" and I "should re-home" roos, instead. Yeah. Good luck with that!!!
If I could learn to do this, I would do it for free for pet owners. It's so sad that people raise a chick from a hatchling in their home or apartment, only to find it crowing one day--and we know what happens to most surplus roos. I'd love to be able to help people keep their pets.
So, if anybody has advice for ME on that, I'd appreciate it no end!!! (I'm dying to get a couple of day-old chicks, or hatch some eggs....)
By the way, you were NOT stupid to think caponizing would stop crowing. It can be hard to find reliable info on the subject! I'm glad you care enough to try. Lots of luck!