My mistake, I thought the term "gray area" just meant it was confusing. After looking it up I now see it means "not readily conforming to an existing set of rules."
But it kind of is a gray area, because there is nothing specifically saying you can or cannot have a handgun in the car at 18. However, after looking at all the surrounding laws in 922 (unlawful acts) and the castle doctrine and on the TN state code, to me it is pretty clear because it doesn't say it's illegal anywhere. Hence why I said it definitely is legal. Its like connecting the dots... one law leads to another
As for the documentation to show the officer, I mean the only documentation that is necessary is exactly what the US code and Tn code says. Thats what the law is. I know an officer would probably not even want to look at it Ive seen videos of people who know what they're doing is lawful and try to provide some documents, but almost always the officer don't wanna listen. What I would like to ask an officer is to show me some documents that says its unlawful... there isn't any. I know asking them those smart ass questions will probably jus get you in cuffs but it's the logical proper way to have an argument.
As you said an argument could be made under 37-17-1316 says its illegal for anyone under 21 to purchase a handgun from a dealer, I mean i don't know how you can defend that argument because handguns are not only bought from FFL dealers, they too brought in a private sale. And as you sated, private sellers can sell handguns to age 18 and up.
I kind of have repeated what others have already said in this thread I know but I couldn't help but comment on this because this topic has been on my mind for a couple years. I always looked up this same question and nobody had specifically asked it until this guy did just a month ago