We let 6 of our Cornish X from the spring go to 6 months to see if there was a difference between processing at 10 - 12 weeks old. The younger the better we have found. The older X's when skinning them were tough and the meat was darker; not only that but the breast size was smaller than the younger ones we had processed; ours were allowed to free range in the yard. We did not weigh the older birds but the younger ones dressed out between 8-10 pounds on 20 % protein feed. The younger ones were kept in a portable chicken tractor. We will always process at 8-12 weeks for sure !!! Just FYI for anyone else who was wondering how the ages compare