If the answer above is None it means there is no specific mention in the legislation, but you still need to ask local law enforcement before drinking in South Africa.
The parent, adult guardian of a minor or a person responsible for administering a religious sacrament, may on occasion supply to that minor a moderate quantity of liquor to be consumed by the minor in the presence and under the supervision of that parent, guardian or other person.
You can find more legal details and links here:
Wikipedia Legal Drinking Page