The author, a well respected consultant to breeders has passed away. His book was self-published, before computers, and I'm not sure whether he had family that re-published any of his material or not.
For new readers who may be interested I've added an image reflecting the info in it. Please respect the copyright on the image (don't copy it!), but the information in it is available to anyone who looks at it. I have a 'helper' now. She does publishing, creates images for me and does other online work, too.
Not that all chickens necessarily die at age seven, but the chart has to stop somewhere, I guess. I just lost a Yokohama hen who had almost reached the age of 16. I once had three Yokohama hens - the one that lived so long is pictured on the top right. She was very tame and sweet.
Back to work on those projects - soon as they're published will link to them, then you'll see how hard I've been working for the past year. 😊