The mishna discusses the stubborn and rebellious son, who according
to the torah is to be executed. When does he become liable? From the
time he grows two (pubic) hairs to the time he grows a "beard" (in that
area). A minor is exempt and the text says "son", not "man", so it can't
refer to a full adult. The g'mara discusses this, bringing arguments about
the age at which a boy can father a child and that this is a good boundary,
but ultimately concludes that he remains eligible for a period of only
three months. Rabbi Shimon also observes that logically this ought to
apply to a daughter too but it is divine decree -- the text says "son",
so it only means "son" and not "daughter". (68b mishna, 69a g'mara)
Someone at the minyan this morning asked who conducts the hair inspection.
The trade-offs would be modesty versus correctness. I don't know, but I
imagine that the father would need to see first before making the accusation
and then to pronounce a guilty verdict the beit din would need to see, but
I could well be wrong. (I am, in part, reasoning from the blasphemy
testimony we talked about a couple weeks ago.) Anyone know?