First week of egg laying!

I have a small backyard flock with 5 pullets: a RIR, a light Brahma, a bantam frizzle cochin, and 2 EEs. My ladies are 18/19 weeks old. Last Tuesday, it finally happened, I got my first egg! And since then, I have gotten 6 eggs in 7 days, and all from a single pullet, the bantam cochin frizzle! Of all the girls, Gretchen would have been my last guess as to who was going to lay first, and I am just as surprised at how prolific she is! Do cochins normally start laying early and often?