Board Thread:Questions and Answers/@comment-37159314-20181117011016/@comment-36009152-20181117173418

Intriguing, and official sources decide all! Like Yu’s Infobox, Shigure and Sayuri would have:

15 (Catastrophe, Chapter 1)

Then underneath:

16 (Catastrophe, Chapter number when they have their birthdays and turn 16)