The sheriff's representative is WRONG.
Can you buy a gun if you are under 21? Yes, if you buy it from a private individual. No, if you are buying it from an FFL (dealer, pawn shop, etc.).
You are required to have a Pistol Purchase Permit from the sheriff for any handgun transaction, including your dad buying it for you. He should buy it for himself; when you get the PPP, he can then "sell" or gift it to you. Without your obtaining the PPP, he would be guilty of a "straw purchase" (getting a gun for someone not able to get it themself).
There is no requirement for paperwork to transfer the gun from your dad to you other than the PPP. You also are not required to actually give the PPP to a private individual, just show that you have one. Only in Durham County is there gun registration.
If the gun is stolen and you report it immediately, complete with make/model/caliber/serial number, then neither you nor your dad would be in the wrong. Unless of course, you had it where you shouldn't, but that's a whole different issue.
Can you carry (OC) a handgun if you are under 21? Yes, absolutely. It also does not have to be yours..
Read 14-402. 403, 404. Print it out, or just write down the reference and show to the person who misinformed you.
You can't buy the ammunition for a handgun until you are 21. bummer
Print out a copy of the NC sticky and carry it with you. Be real familiar with NCGS Chapter 14.