I have been trying to integrate my younger chickens with my older chickens since they were about 7 weeks, I can't sum up everything that I have tried in a short blurb, but I can say that Iv'e tried alot of different approaches.
I probably should have waited until they were older to start the actual integration because of the type of set up I have.
Iv'e come to the conclusion that, if your in a free range situation, you can integrate at a younger age.
At this point one of the younger ones is finally starting to be ok with the older flock, but at the same time that is happening, the other younger one is getting more and more afraid of the older ones and has retreated from the run into the coop house.
She has been hideing in the coop house for the last few days, ocassionally one of the older ones goes in there to lay an egg and chases her out.
They are 17 weeks old today, the older ones are 8 weeks older then the younger ones.
Thats the short version, for the longer one you may need a speed reading coarse lol
I'll have pics for the week in a few.