Yep, you posted in the right place - your questions are Idaho specific.
18 is the legal age to OC a properly holstered handgun in your state.
See OCDO interactive maps and links:
Caution: avoid links offering things for sale as your reference to "Call of Duty" did - that is a sure way to get banned - not to be harsh, but you have attracted a Moderator's attention.
Also long guns are generally OT on OCDO except in the General Discussion forum - carry is not encouraged. Please read the rules first - http://forum.opencarry.org/forums/misc.php?do=showrules
Other than that, welcome to OCDO - hope you stay, enjoy and profit.