a ballad country song from Morgan Wallen that talks about a timeline 7 summers or 7 years ago, although country girls can't really help fall in love with him because of this song. It does look similar to 7 years by Lukas Graham.
The Rule is an acknowledgment of one's own mortality and is invoked as a means of avoiding activities, people, movies, organizations, books and TV shows that are very likely a total waste of time.
In essence, it means that each of us only have a finite number of summers left, and those summers aren't to be frittered away on meaningless crap.