Your birds are young, not all of them have started to lay just yet....just as with humans, they all develop and mature at their own pace. As an example, in my current flock I have 15 pullets -- one started laying six days ago and has laid four eggs, one has laid two eggs in that same time and the other 13 are not yet laying (though there are 4-5 who are so close I can almost taste the eggs). All these birds are the same age, but some have matured faster than others. What breed(s) do you have?
2 white, 3 red, ended up with one white rooster. All were to be female!! Ha
