I don't think you can but G Suite groups can include other groups as well as users so you can add different groups in an "everyone" group to make managing everything easier.
If your goal is to search for old or the oldest post by a particular author in a given group, show activity may help:
Search for the author (in your group)
Select a post from the author
The down arrow in the post contains the "show activity" menu item
See in which month the author has posted
Select the month in question
If you have different selection ...