chrisbohman
Chirping
Girls that started laying in December, interesting. What breeds were those girls? I have 2 girls that are not yet laying, the first is a 25 week old Easter Egger, the 2nd is a 26 or 27 week old hen called an Americauna, but from what I have since deduced is most likely a different variety of Easter Egger.I see no reason to panic or worry. I've had a couple of pullets start laying as young as 16 weeks. I've had a couple start laying at 9 months in early December on some of the shortest days of the year. I consider both of these as extremes but not that unusual. They are going to lay when they lay. External circumstances can affect that but each is an individual.
What I often see in a group of 10 dual-purpose pullets like Sussex is that by 20 weeks one or two will probably be laying. By 24 weeks of age I'd expect maybe half to be laying. By 28 weeks old I'd expect all of them or practically all of them to be laying. But each one is an individual and can be an exception. But each flock is unique and can vary quite a bit.
As all the others are laying you are not doing anything wrong. It is not a flockwide problem. If you even consider it a problem it is an individual hen problem. If you feel you have to do something do it to that individual hen. Do not risk messing up the rest of your flock by treating them all.