I know this is not much help, but 16-40 weeks! The initial pullets I bought were 8-10 months old before they started laying (in the winter). Chicks from my eggs (from those hens) have started as early as 16 weeks. Mostly as chicken people, we wait. Wait for the hatch, wait for the sexing, wait for the laying...wait, wait, wait!
Ha! I know all about the waiting. My Marans finally started laying at 23 weeks. We are getting nice dark eggs. Unfortunately, while they started laying in the nesting box, one has developed the bad habit of laying the egg wherever she is standing, usually in the run. Which is even more challenging because her eggs are all ready the color of dirt! Hopefully it's just a phase.