S.C. Code Ann. § 15-1-320

(a) All references to minors in the law of this State shall after February 6, 1975, be deemed to mean persons under the age of eighteen years except in laws relating to the sale of alcoholic beverages; provided, however, that any person performing any act or receiving any property, rights or responsibilities pursuant to an instrument executed prior to February 6, 1975, shall have his majority or minority determined by the law relating to majority or minority in existence at the time of the execution of such instrument. (b) Persons executing wills, trusts and deeds prior to February 6, 1975, shall be presumed to have intended that minors were persons under the age of twenty-one years in the absence of facts which would indicate a contrary intention.