Should not be too hard to find the ND statutes on gun purchase, below is the NRA-ILA synopsis of the ND law. It looks like from this that ND is like the majority of states where you can privately sell a handgun to someone 18 or over but a FFL cannot. But check the ND statutes. www.handgunlaw.us
also list the minimum possesion age for handguns as 18. That is also the minimum age for applying for a permit.
It is unlawful to sell a handgun to a minor. However, this does not prohibit a person from lending or giving a handgun to a minor if he or she will be using the handgun under direct supervision of an adult. No person may transfer a handgun to any person who the transferor knows or has reasonable cause to believe is prohibited from possessing a firearm. It is unlawful to supply a firearm or ammunition to, or procure or receive a firearm or ammunition for; a person prohibited from receiving it if the transferor knows or has reasonable cause to believe that such person is prohibited from receiving or possessing it.