Red Nara - Chapter 135

... speed! Quickly healing my twisted nose and the bump starting to form on my forehead, I got up and shook myself off. This was the sixth attempt to master the technique of fast movement under Saya's supervision. After she fully recovered, which took about six months, I hitched her up for full-fledged training sessions in any free time, including techniques that are mainly taught to chunin and jonin.

Children under thirteen or fourteen simply don't have developed enough bodies to withstand ...