Mine laid the first real egg in the nest box at 17 weeks. I thought I'd seen some soft shells that resembled egg shells in their bedding and until she repeated laying soft shelled eggs after the first real hard-shelled egg, I couldn't confirm it was, indeed, an egg shell. So she may have started laying around 16 weeks but soft shelled eggs that broke and I never saw them.
Usually around 22-24 weeks of age approximately 6 months.
My rhode island reds are 4 months old and are laying eggs every other day, I was told that they lay at 6 months, but that is not the case with this flock!
Around 20 weeks
2 weeks old thats when mine started laying