So he’s a young dude, playing an old dude, who is now playing a young girl—who is still that old dude.
The novel series began in 2012 and is ongoing with thirteen volumes in print so far by Hirotsugu Ryusen.
The series has Keitaro Motonaga directing it based on the scripts overseen by Takamitsu Kouno.
Going with the English title of She Professed Herself Pupil of the Wise Man, The series was set as a Funimation exclusive for streaming later in 2021 but was pushed back to January 2022.