I believe adult is over 1 year; most start laying at about 4-6 month old. I have only dual purpose breeds, so their temperaments are very similar.
At 4 weeks old I put my youngest out in a dog pen, they could see other chickens in another run or be surrounded when those were free ranging. After several weeks I let them out to free range also, with a small patch of brambles to retreat to as necessary. A few days later I put them in the coop at dusk with the youngest group of hens 3m and 4m olds. THey were terrified. It's taken a few days to adjust. The first day they didn't leave the area of the new coop and hid under the branches of a hemlock. THe next day they seemed to have forgotten how to leave the coop.
It's only been a few days and the girls (now 7 weeks old)race out with the older hens and find their way back during the day (food and water there) and again at dusk. Just my experience. Hope it helps you.