What Age Can Chicks Be Put With Chickens?

Thats a tricky one. You want to make sure they are large enough that they can get away from the older chickens. They need to be feathered out really well. You can make a small pen the keep them in so the other chickens can walk around them and get used to them as part of the flock before turning them loose with the main group. Thats what I did, and mine are doing well. Most of the time my little guys go right through the wire of my chicken pen and do they're own thing and go back to the coop at night to roost with the big guys.  

I have never put young chicks with older ones until 5 -6 weeks old (8 weeks if it's cooler weather). Even then I made a "safe haven" for them to get away from the older ones. I used utility fencing and left a little hole that the young chicks can get in and out of safely but not big enough for the big ones to enter. Make sure if you do this, they have their own water and food supply in case they aren't brave enough to go out with the older ones. I leave this pen in there until the older chickens and the bigger chickens are well adjusted to one another. For me it was 2-3 weeks.