According to the laws of South Carolina, you must be at least 18 years of age to purchase a handgun.  However, Federal law forbids gun stores from selling handguns to anyone under the age of 21. 

Under South Carolina law, no one under the age of 21 can carry a handgun.  If someone under the age of 21 did have a handgun, he or she would be committing a misdemeanor and would face up to $1,000 in fines and up to 1 year in jail. 

S.C. Code Sections 16-23-20 and 16-23-50.