I agree with you on everything but your first point. It's just as reasonable to assume an old domain has fresh content as a new domain, there's no connection be

I agree with you on everything but your first point. It's just as reasonable to assume an old domain has fresh content as a new domain, there's no connection between domain age and how fresh the content is on it/how active it is. Look at Reddit, or for that matter HN. Older domains, fresh content every second. But yeah, old domains basically have had more time to accumulate trust/links/shares/content, so they're more likely to do better in the search engines.