I've blended chicks from different age groups. I started with 28 BR and when they were 3 weeks old I had the opportunity to pick up 10 chicks that were leftover from a feed store order. (4 Buffs, 1 BR, 1 RIR, 2 Americana, 1 Golden, & 1 Blk sexlink) Hubby divided the brooder so that the babies had their own space and the older ones were kept seperate from them. It was still kinda chilly here so I didn't want to move them outside yet. When the BR's were 5 weeks old I moved them out to the hen house and took out the divider for the babies. Last week I brought the babies out to the henhouse and made them an area where they could escape from the older chicks if need be. They are now 5 & 8 weeks, occasionally one of the BR's will chase a baby and try to grab the tail feathers (No damage has been done) but I have also seen a baby chase the older ones. At this point in the morning when I let them out of the hen house, I close the door for about 1 1/2 hours to give the babies free roam in the coop without the older ones around, (I put water & feed inside and out), for the rest of the day the house is open to all and the babies are starting to come outside an investigate finally. Good luck to you on blending yours.