Stories are only partly chronological. The stories are grouped per user and in these groups they are chronological. However these groups are not chronological.

Secondly, posts are not for old people. Posts serve a different purpose than stories. The barrier to post is a lot higher, and they are definitely not used (anymore) to share that you are going to a restaurant/movie/etc, because stories took over that niche. However something like a (single!) post with (multiple) photos of your last holiday (with at least the first one including you) and some fun caption is still totally done.