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Eight months isn't too old

Eight months isn't too old for some chicken breeds.
Are they free-range? Chickens do best eating naturally--with grass, bugs, and other foraged material.
You sound as you have a good mix of nutrition. It's important for chickens to get a minimum of 16% protein.  We've never fed eggs to our chickens. We use soybeans, worms, and yogurt mixed with whole grains (not corn). You may find this page helpful: http://www.lionsgrip.com/protein.html