You have to be 21 when purchasing a handgun from an FFL.
However, private sales/transfers to persons lawfully 18+ on own a firearm in SC.
For drivers, the law states "a person."
Sounds legal if they are old enough to drive themselves with exception of certain places prohibited i.e. in the vehicle on schools ground w/o a CWP.
I don't know anywhere it is specifically prohibited for a lawful driver regardless of age to have a weapon in the console.
SECTION 16-23-20. Unlawful carrying of handgun; exceptions. [SC ST SEC 16-23-20]
It is unlawful for anyone to carry about the person any handgun, whether concealed or not, except as follows, unless otherwise specifically prohibited by law:
(9) a person in a vehicle if the handgun is:
(a) secured in a closed glove compartment, closed console, closed trunk, or in a closed container secured by an integral fastener and transported in the luggage compartment of the vehicle; however, this item is not violated if the glove compartment, console, or trunk is opened in the presence of a law enforcement officer for the sole purpose of retrieving a driver's license, registration, or proof of insurance;
SECTION 16-23-30. Sale or delivery of handgun to and possession by certain persons unlawful; stolen handguns.
(A) It is unlawful for a person to knowingly sell, offer to sell, deliver, lease, rent, barter, exchange, or transport for sale into this State any handgun to:
(3) a person under the age of eighteen, but this shall not apply to the issue of handguns to members of the Armed Forces of the United States, active or reserve, National Guard, State Militia, or R. O. T. C., when on duty or training or the temporary loan of handguns for instructions under the immediate supervision of a parent or adult instructor; or