In cases where a person wishes to reside in South Africa for a prolonged period without working or studying, it is possible to obtain Permanent Residence on the grounds of financial independence.
In such cases, the applicant needs to prove a net worth of at least ZAR12,000,000, and also needs to pay a fee of ZAR120,000 to the Department of Home Affairs on receipt of the Permit.
The purpose of the qualification criteria seems to be to ensure that only persons who are genuinely self-supporting financially are allowed access to the country on this basis. Age is not a factor in submitting your application. However, if you do not possess the extensive financial resources required for this type of Residence, or if you simply do not want to apply in this way, it may be worth your while to research the option of applying for the permit specifically designed for retired persons, even if you are not retired or of retirement age.