I am a va resident but often go to tennessee. is it legal for me to have my glock (loaded) inside my truck? can i be in possession of a shotgun or rifle- unloaded? I am under 21 yrs of age.
In Tennessee, the "age 18-20, but under 21" stuff comes in to play in two scenarios: you can't apply for a TN handgun carry permit (since you're a non-resident, you couldn't apply anyway), and you can't purchage a handgun or handgun ammo from a licensed dealer (federal law). Since I would assume you already have the gun and ammo in question, and since TN recognizes all permits regardless of age or requirements to get it, neither of these apply.
However, like the other people said, TN doesn't allow any form of unlicensed carry, whether on foot or in the car, open or concealed. When transporting it in a car, it can't be concealed on or about the person; the ammo and gun must be separate; and the gun/ammo can't be "readily accessible." While this is somewhat up to the interpretation of the cop on the scene, it is recommended that persons without a permit transport it in the trunk or very back of the vehicle (if the latter, a lock on the case, while not expressly required, does make it less likely that an officer would construe it as "readily accessible").
If you want to carry one loaded, I would suggest you get a non-resident permit from New Hampshire or Maine (they are two of the six states that will unconditionally offer permits to those age 18-20). Be careful about carrying in other states besides TN that "reciprocate" that state. As an example, Florida recognizes New Hampshire but requires that it's holder be age 21+ and a resident.