What is the origin of the term "Tyro" for inexperienced pilots? Over the years I have been aware of the term "Tyro" to mean a new or inexperienced pilot. I'm pretty sure it is/was used more in a military setting than a GA one, but none the less I was interested to know if anyone knows the origin of this term, and the reason why it is used? Is it still used commonly? 

This may be a term only used in the RAF, I don't know.
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