On average, pullets, or juvenile hens, start laying eggs at about 6 months of age, depending on the breed. The heavier breeds such as orpingtons or marans generally start later than the lighter breeds like leghorns or hybrid types.
A few signs as to when a chicken will begin to lay eggs are: the wattles enlarge and turn red, the comb becomes a deep red and enlarges, they may start to sing the I'm-about-to-lay-an-egg song a few weeks in advance, if you stand over them or if you put your hand on their back and they squat down on the ground. They do this if a cockerel is going to mate them, which indicates that they have, or are very close to reaching sexual maturity i.e. they're going to start laying!!! The most likely thing to happen of course if for you to go and collect the eggs one day and discover an extra egg in the nest box. My cream legbars have just started laying and I am so pleased!!!! Keep your eyes peeled for photos on Facebook: https://www.facebook.com/Growing-Pains-Parsnips-to-Poultry-987143211307918/ and Twitter: https://twitter.com/Grow_Pains