Age of Wisdom
From Guild of Archivists
The Age of Wisdom was the 125th year of a D'ni person. After that age, the person was considered to have acquired wisdom, had the right to counsel others, and could become a Grand Master or Great Lord.
Advisers who served the Kings had to have reached that age, and a king under the Age of Wisdom had to have an adviser. (The sole exception was Ahlsendar.)
See also
References
DRC. Maturity notebook. Uru: Ages Beyond Myst, Myst Online: Uru Live.