This depends on the type of retirement fund/s that you are a member of.
Discretionary investments (non-retirement fund investments):
You can retire at any age.
Pension-, and Provident Funds:
If you are a member of a pension and / or provident fund (you can be a member of both) your retirement age is determined by the rules of the specific fund.
It is around age 62 to 65 for most funds.
Your retirement fund rules may make provision for early retirement from age 55 onwards. In the event of permanent disability the fund rules usually stipulate that you may take early retirement at any age.
Pension-, and Provident Preservation Funds:
Anytime after age 55.
Dependent on the fund rules but the member could be entitled to a withdrawal benefit if he /she is disabled and unemployed, or the member will be entitled to an ill-health early retirement benefit, should the trustees find him / her disabled.
Retirement Annuities:
Please note that your retirement date from a retirement annuity/ies is NOT linked to your retirement date from a Pension-, and / or Provident Fund.
You may retiree from age 55 onwards and postpone you retirement date as long as you like / need to. Even if your retirement annuity contract has a stipulated retirement age after age 55 e.g. 65 you may retire from age 55 onwards. However, because you have taken early retirement your fund value may incur penalties.
The elephant of the room is whether you have saved sufficiently for retirement. This, to a large extent will determine when you can and should retire from your retirement annuity/ies. As a general rule we advise client to work a long as they can.