Just out of curiosity, what is the earliest you have had a pullet start laying?
My earliest layer was one of my red sex links-she laid at 18 weeks exactly. My other red laid two days later, followed a week later by one of the black sex links.So all of them were laying by the beginning of May. My other black sex link just started laying a week or so ago! They are all the same age so it just depends on the chicken.