I've had hens for about 10 years now, mostly for our own egg source. I've had as many as 25 at one time, but as life has happened, right now my flock has aged out and I'm down to two which lay when they feel like it. I found a guy with month old pullets for sale for a fair price, but it's the dead of winter and I have no other place for them but the unheated coop. Are they too young, and what is the minimum age for winter survival?