I just converted a WordPress website to Sydney. I found the setting to turn commenting off new posts, but not where to turn them off from old posts. Not possible?
I found a way using WP bulk edit, works for posts and pages. https://wordpress.org/ideas/topic/turn-comments-onoff-for-multiple-posts-at-once
Would be nice feature in Theme settings.
I am glad to know that you have been able to manage it by yourself. Please let us know in a new topic if you have any further questions, or if we can provide you with any other assistance.