Agree, except:So, thinking over my criteria,
4. Age -- I won't progress my flock if I don't replace the older birds with the next generation.
--it's only true if the next generation are better than the older birds. Otherwise, you could make "progress" in the wrong direction.
--if you want to breed for longevity, then you should keep each bird just as long as it continues to perform well. That way you'll end up hatching the most chicks from the ones that perform well for the most years. (Whether you care about longevity is up to you. I'm only commenting about what to do IF you care.)