Kenji covered hard boiling eggs with scientific rigor: https://www.seriouseats.com/the-secrets-to-peeling-hard-boil...

We have backyard chickens and hard-boil a lot of eggs. The biggest effect on peel-ability: Start with boiling water, do not start the eggs in cold water.

For years I started with cold water because that's what Alton Brown said to do in Good Eats. And for years the eggs were a pain to peel. When I read Kenji's article, I switched, and immediately eggs became much easier to peel. Night and day.

No other factor comes close in terms of effect. Not age, not backyard vs store bought. Not the breed (at least, not for any of the dozen chicken breeds we have had). Start with boiling water and 9/10 eggs peel nicely, start with cold water and 9/10 eggs peel terribly.