Really? Eleven to twelve weeks old isn't too old to perform the procedure?
I concur with Ron - I like to do mine in the 8 - 12 week old window, but my first batch ended up being 14 and 15 weeks old due to weather and scheduling back in April. The thing about doing cockerels in puberty is the testes will break up easier, and it's more likely to leave enough behind to regrow. Out of the ten I did in April, at least 8 are slips, but that was three months of chicken harmony before the slips started showing again a couple weeks ago. They also have doubled in size from when caponized, and will have much more meat.Surely you jest? That's the ideal age for a beginner to start with and in just 5 or 6 months, they will fantastic table birds!