Only 9 months old. She's gone a bit broody after that, but cutting her a bit of slack because of this. (after all OUCHIE!!!). Australorps from Table Top Australorps NSW, Australia. Beuatiful, beautiful ladies.
It's my understanding it is similar to a double yolker in the one respect the double yolks one yolk does not "move forward" so to speak in the hen's "assembly line" and the egg in an egg is where the egg is formed and then backs up in the hen's "assembly line" meets the other yolk and the hen's body does what it's supposed to do but accidentaly captures the other egg with the yolk and envelops both. Sorry I made my explanation kinda odd, but I am keeping it "family friendly" so trying to word it so an 8 year old's (as an example) parent's won't get mad...