A prevalent theory in the One Piece fandom suggests the Five Elders are immortal. If they are, they likely became so through the Immortality Operation of the Op-Op Fruit; there aren't many other known ways to become immortal in One Piece. Whatever happened must have halted their aging process and allowed them to rule through the World Government for as long as they wanted. Since the World Government has been around for 800 years, many assume these Celestial Dragons have been running it since then. Unfortunately, there has been little concrete evidence to back this theory, so it remained speculative.
Source：https://www.cbr.com/one-piece-chapter-1095-saturn-immortal-hints/
