Here is the age he has just been promoted.

First-level: twenty-one years old. Promoted before going to the Mist Forest to perform a resident mission.

Level 2: Twenty-four. Promoted during missions in the Mist Forest.

Level 3: Twenty-eight years old. Promoted in the Bloody Fortress.

Level 4: Forty-two years old. Promoted at the death garrison under the Bloody Fortress.

Level 5: I don’t know yet! Hehe!\
Chapter completed!