I have some more mixed-breed chicks that I hope to caponize as soon as I can find the time. They're about 7 weeks old now, and I'm fairly certain I can tell their sex with accuracy. Growinupinfl, that's a great picture you posted, but that's not what you're going to be seeing in the small incision you'll need to make to caponize your birds. You'll need to make an opening into their body cavity and look up towards the spine to find the tiny little bean of a testicle surrounded by loops of intestine. It can be difficult to tell the difference between testicle & intestine, you don't want to try to remove the wrong thing. I know that some folks can remove both testicles from one side, I feel that I'm doing well to do one per incision.
I'm hoping to see a difference in the birds I caponize at a younger age, the trouble right now will be finding the time in my schedule in the next few weeks. But I also fear that it will be a more difficult operation, to locate their smaller organs. I'm going to get a light that can be strapped to my forehead, and those beading tweezers, to see if that will make things easier.