Average age for point of lay?

What is the average age in weeks that a pullet will start to lay. I've seen different ages. Some say 20 wks. Some say 24 wks. Etc. Etc. I have three birds (SS) that are 24 wks as of Monday, and six birds (3 BR and 3 BO) that are 22 wks as of yesterday. I am getting 3 to 4 eggs a day from 2 of the specks and one each (sometimes one sometimes both) of the BR and BO. I know that each pullet has her own internal clock for when she will start producing, but I thought we would be getting 7 to 9 per day by this time, but maybe I'm mistaken. Thoughts anyone? Not seeing any evidence of broken eggs in the boxes or coop floor either.