Hens still not laying

[Thedogsbark]

My two hens will be thirty-three weeks old tomorrow. They have yet to start laying. My ducks, which are three weeks younger, began laying quite a while ago. So why have the chickens not started laying yet? Is there anything in particular I should be doing or giving them? I don't give them oyster shells currently because I wasn't sure if I should wait until they start laying to give them.
A week or two ago one of them had started clucking like she was about to laying an egg. She clucked for two days, then stopped. No eggs. I'm not sure why she was clucking. She suddenly turned a little aggressive towards me lately though. She isn't aggressive towards the other hen, just me. She peaks me as hard as she can and tries to jump up and attack my hands if they're above her. I don't know if about to be laying is supposed to make them more aggressive. I was thinking maybe they're waiting until spring comes around to start laying? I was convinced that that was what they were doing, then one started clucking like the chickens around us when they lay eggs.

 

[ChickenCanoe]

16 more days and days will start to lengthen. That's what they're waiting for.

 

[rjohns39]

They'll lay when they're ready. Some will wait until spring while others will start mid winter. Feel happy that the ducks have started as they generally wait until spring.

I just read @ChickenCanoe 's post... and didn't even realize we're that close to the solstice.