I’ve had pullets of various breeds begin laying as young as 16 weeks. I’ve had some pullets wait 9 months before they laid their first egg. It varies by the individual. Breed and time of year come into play too but mainly it varies by the individual. How you feed them plays a part too. If you feed a high protein feed, you can often push them into laying a bit early, but that is not always healthy.
You really don’t have enough for averages to mean a lot, it varies so much by the individual. If you had twice as many I’d kind of start looking for the first egg around 20 weeks, maybe 18 weeks if one is a bit early. It’s possible but unlikely before that. If you had twice as many, I’d think a few more would kick in about 23 to 24 weeks, with the majority laying by 7 months. But this is just a guess. It really can vary by individual pullet.