Hell I don't know and moreover don't care. Probably comes from Jewish law. But it's tangential to the issue, pick whichever age you like. Pretty much common sense. In American law the age varies by state. In my state a child cannot be held responsible for his actions before the age of ten. (Parents may be liable through the tort of negligent supervision)
The key elements in human thinking are not numbers but labels of fuzzy sets. -- L. Zadeh
