My first EE laid at 18 weeks then 3 more started the following week. My husband thinks its all the treats that i give. I have never missed a day of giving them treats or scraps...most days they get something 3 times a day.
They love wheat seed, grapes, noodles, raisins, apples, lettuce, squash, bread,cereal, oatmeal, corn on the cob our of the garden, stuff like that. They are let out to free range each evening for 2 to 3 hours before bedtime.
Ive heard that you dont want your chickens to lay to early though so if you are still waiting for eggs, keep in the back of your mind it might be more healthy for them in the long run.