Most chickens lay around 4,5,and 6 months.Some lay as early as 3 months.....But some also may wait until their nearly a year old.
Some ways to know, is their combs and wattles will begin growing.They will also have more red faces and combs.Their vents will also begin getting bigger and a more "Reddish" color.
They will also squat.The submissive squat is when they lay flat,and spread their wings out.Hens without a rooster will do that if you approach them.If they are doing this they should be laying in either less then a week or in about a week.
Most of my chickens have started around 4 and 5 months,maybe a little later.But a lot of these are duel purpose chickens and egg laying kind.
One was a (small) brown double yolker, and the other was a nice speckled egg. The clues were the past week or so they were starting to squat for me when I went in their run, and also their combs and wattles were getting very red! I wonder too if it matters that I had to switch from an 18% protien feed (Nutrena Chick Starter), to a 20% protein all flock starter (Klambach) because my local feed store could not supply the one I normally got. It seems this batch of pullets is starting to lay earlier than batches I have had in the past which were usually around 5 months...but those were different breeds also (Australorp). Hoping the growth isn't too fast 
