I have 4 white Leghorns, they were presumably all hatched the same time because we picked them up from a hatchery as day-old chicks. One start laying at 21 weeks, then one more chicken joined in each subsequent week till they are laying consistently at 24 weeks.
Mine did exhibit the maturing signs such as the red wattle, comb and face and was squatting before start laying eggs. AT 19 weeks, I switched from grower to layer feed, opened the nest box and put in a fake egg. Even though they were a bit late in laying comparing to others, I was able to squeeze in a cycle of deworm medicine just before they all laying consistently so to minimize wasting eggs.
It is recommended that chickens be dewormed twice a year (say spring and fall), give them two rounds of medication (such as 0.5 cc of Valbazen by mouth per Leghorn), 10 days apart then discard eggs for 14 more days after the last medication. That's 24 days of no eating eggs! So if your chickens haven't lay yet but close to do so, take this opportunity to deworm them.
