What is the origin of the term "Tyro" for inexperienced pilots?
It's just a synonym of novice, it is used outside of aviation. Like many other aviation terms (e.g. pilot) its origins precede the first manned flight and it was and is used for non-aviation novices. Aviators borrowed many existing terms.

tyro (n.)
1610s, from Medieval Latin tyro, variant of Latin tiro (plural tirones) 
"young soldier, recruit, beginner," of unknown origin.


http://www.etymonline.com/index.php?term=tyro