The main character is awarded the title of sage, along with four other people, but then discovers that he is in fact attributeless, and that the younger generation will surpass him with less effort. Then he dies and is reincarnated into the body of a child of his own family, but years in the future, and discovers that he still has all his abilities, and that the magic of that world regressed. What's the name of this manga...?
I believe this is The Unsuccessful yet Academically Unparalleled Sage, also the answer to this question.
The main character was considered one of the most powerful magic users in the country. One of the other powerful mages creates a test to determine compatibility with types of magic where you put some hair in some magic water. The main character then found out he had no compatibility with any of the elements. Then he dies and is reincarnated as one of his descendants. Once he remembers, he tests out his past life he tests out his magic. He then finds out his magic is as powerful as it was in his previous life, despite still having no compatibility.
He does some training with one of his older brothers, who mentions that level 4 magic is very high level. The main character thinks to himself that level 4 is a low ranking sorcery. He then makes a chart to compare what he thinks the magic levels should be, compared with what his brother said. All the categories ended up off by a couple categories. What he considered Low magic, the new time considers Super High level magic.