I actually have a different issue and got a lot of help on the question of birds going outside. I happen to have 4-- 4 week old chicks in a dog crate outside with 2-- 8 week old pullets. They have one of those holland warmers (square with heat emanating from top down). All birds have been doing great outside, but even the older pullets go under the warmer at night. (The dog crate is in a covered shack (open on one end) which also houses my coop with 6 adult layers. The adult layers also free range all day.
From reading the other site, I'm going to add the two pullets to my adults Wednesday night, and leave the four chicks in the crate for another couple of weeks. My temperatures here over the next week will be 60's during the day and 40-50 overnight. I really need to get the two fully feathered pullets out from under the heater. Thanks.
I think he is using "juvenile" to mean fully feathered Pullet.