Sounds neat Linda! I hope someone who knows this method sees this and shares it with us, because I am real curious how it works.
Otherwise, one way I know to measure a hen's approximate age is to look at her shanks. Younger birds have smooth legs, where as older birds' legs are rougher, and sometimes thicker. The legs usually don’t lie…but they don’t help much beyond 2 years of age either. Some chooks age really well, where as others not so much. Kinda like people I suppose.