Enlightened

Human sages are those humans that have spent a very long time training their abilities and honing their skills.

Specific requirements for attaining Sage hood have not been detailed, but they seem to involve living for a very long time and having specific qualities (similar to how demons need to have specific qualities to have the demon lord's seed).

Human sages also have very strong wills and thus are much more difficult for demons to manipulate or to crush their hearts.

Many of the strongest warriors have risen to the rank of Human Sage.

They also seem to retain the strength comparable to Arch Demon and incredible longevity of humans.

Personality
Human sages typically are less prone to emotional swings and tend to have a keen intellect. Their vast battle experience and calm minds allow them to be deadly on the battle field and very good at analyzing situations off of the battle field.

Abilities
Human sages are known to have very high battle abilities, but the actual skills they wield will vary greatly.

They seem to be able to take advantage of the abilities of God Class Armor and Weapons.

Known Human Sages
The Seven Celestial Sage

Rudra's Royal Knight No.3 to 10