What's the latest Age to incorporate flocks?

[Kye022984]

I had two shipments of chicks within a week apart. The flock that is a week older is four weeks now and the other is three weeks. We just put a wall of chicken wire in-between them so they can see each other but aren't in the same brooders. When is it too late to have them in the same brooder/tractor without having them fight each other?

 

[ChickenCanoe]

The sooner they go together the better it will go. I'd put them together now.
I wait till they're about 3 days old and mobile and then integrate even if the others are up to 6 weeks older.
A lot has to do with space.