I want to fly with a 5 months infant, from Johannesburg to Cape Town. Does an infant under six months need a ticket?
If the infant is going to be held in your lap for the entire flight, then they are charged the infant rate. SAA charges about 10% of the adult fare for an infant flying domestically.
If you are bringing a car seat for the infant to use during the flight, they would need their own seat and would be charged more for the seat (child's fare).
Other carriers may have different policies, you need to check their websites for details.