Some of us may be using different concepts of "maturing." There is the time it takes to begin to lay, the time it takes to flesh out enough for meat, and the time it takes to finish out in growth/show potential. They are not the same time points.
My birds began laying at 4-5 months old but I did not consider them "mature" at that point. More like teenagers who finally got after-school jobs and took some of the pressure off the cost of raising them
The cockerels are still filling out at nearly one year of age, but the quality of the bone structure was evident from about 6 months. This is my first year with the breed. I'm guessing they won't have reached their full potential for another 6-12 months. So I consider these birds slow to mature, but they have been earning some of their keep in terms of eggs and meat since they were about 4 months old. I'm happy.
Sarah
My birds began laying at 4-5 months old but I did not consider them "mature" at that point. More like teenagers who finally got after-school jobs and took some of the pressure off the cost of raising them

The cockerels are still filling out at nearly one year of age, but the quality of the bone structure was evident from about 6 months. This is my first year with the breed. I'm guessing they won't have reached their full potential for another 6-12 months. So I consider these birds slow to mature, but they have been earning some of their keep in terms of eggs and meat since they were about 4 months old. I'm happy.
Sarah