I have 3 hens that are about 4 months old, full size and about ready to lay. Then I got 10 more chicks that are now about 6 weeks old. They are feathered and they are all outside. The chick's tractor is inside the big girl's run. I will be needing to combine them in the next few weeks due to space restrictions in the tractor. I've read some places that they need to be the same size when introduced and then I've read the younger the better. Anyone have experience with this?