Niddah 52 - Two Hairs
We already mentioned that a sign of physical maturity and becoming legally adult, for a bat- and bar-mitzvah are two hairs . There are multiple opinions on where these hairs must be, but the accepted view is that they must be in the pubic area. At this time, the girl can perform the ritual of yibum or halitzah , and the boy becomes eligible for the punishment of a rebellious son . He stops being punishable as a rebellious son when his beard grows around. This really means the bottom (pubic) beard, and only a first ring of hair there, but the Sages employed a euphemism.
Two hairs are also found in the laws of red heifer , where the cow must have no more than two non-red hairs, and in the laws of spiritual leprosy, where two hairs in the affected area turning white indicate the affliction. How long do the hairs have to be? Enough to bend their top to the root - these are the words of Rabbi Ishmael. Rabbi Elazar says, long enough to be grabbed by a fingernail. Rabbi Akiva says, long enough to be removed with a scissors. And the law? It follows all views for stringency. This means that once the shortest length is reached, the child is not a child anymore, but to become full adult, they wait till the hairs are of the largest size of those mentioned above.
Art: Adrian Scott Stokes - Portrait of a young boy and girl, three-quarter lengths