8 weeks old chicken laying eggs

[Biggeda]

I have 13 eight week old chickens and one is laying full size eggs. I have raised chickens for 7 years and this has never happened. They dont look big enough and still on start and grow feed. They are in a coop where no other chickens can get in. Not sure which one is doing it. I checked my records on when they were hatched which was 8 weeks and 4 days ago. I have gotten 1 egg for the past 3 days. Is this possible? I can't find an answer. I'm 100% sure its one of them. They are a mixed breed. I live in Texas, not sure what other questions you may have. It's odd to me. oh, and no I'm not crazy promise.

 

[CluckerFamily]

What is in the mixed breed?
I don’t have high production breeds but I’m wondering if that is part of the mix. It is odd.