I am not a lawyer. Call a lawyer to confirm that it is allowed.
I do not see anything in the statutes that prohibits you from carrying openly. However, there is the issue of unlawful transfer of a handgun to a minor. http://www.mainelegislature.org/legi...Asec554-B.html
If I'm reading it right whoever gives you the handgun is breaking the law. Technically you are not breaking the law being in possession of the firearm, but whoever gave you the firearm is gonna get in trouble.
So I would not recommend carrying until you're 18. You legally can't yet own a glock. Sorry.