I've had some hens molt in fall and others in spring. It all depends on the lighting situation, I think the shorter days during the fall/winter trigger hens to molt naturally. If you keep a light on them during the winter to extend the daytime hours they will molt in the spring. I don't think that it makes a difference when they molt, but if you want a decent amount of eggs in the winter then they need a light.
My hens have only molted once in a year.
I don't think breed or age has anything to do with it, but in the spring my hens from the lighted coop will start to molt with the warmer weather. Unfortunately, we get a lot of rain and they tend to get drenched.
All chickens molt differently. The healthy good quality birds usually molt fast, while the lesser quality birds will take longer.
A molting hen will usually loose feathers over most of her body. My hens normally start out with all head feathers, most of the neck feathers, and a lot of butt fluff falling out at the same time. You can definitley tell they're molting when you can see the pin feathers coming up through the skin.
An over bred hen will usually only be missing feathers on her back just infront of her tail and on the back of her neck or head where the roosters grabbs feathers with his beak while mating. And a picken on hen will probably only have bald spots on a spot or two of her body. (I had one that went around and plucked out the other hens butt fluff and ate it.
There were never any pin feathers though so I knew it was not a molt.)
Hope this helps a little!
