I know that Idaho is a "shall-issue" state if you're 21 or older. They also allow for permits <21 y/o based on the sheriff's judgment (Idaho Statues, Ch 33 Section 18-3302.11):
Does anyone know if they ever actually do issue for solid 19 year-olds? And if so, what might some of the factors be which the sheriff might consider?(11) The sheriff of a county may issue a license to carry a concealed weapon to those individuals between the ages of eighteen (18) and twenty-one (21) years who in the judgment of the sheriff warrant the issuance of the license to carry a concealed weapon. Such issuance shall be subject to limitations which the issuing authority deems appropriate.
My daughter will be moving there soon, and I would prefer that she carry if possible. The sheriff there is a solid 2A supporter (and NRA instructor), but I don't want to step on toes by applying if it never happens in the real world.