Specific age of onset data is not found for South Africa; however, globally, age is identified as an important risk factor with the risk of developing dementia reported by the 10/66 Group as increasing for those 60 years and over in 21 Global Burden of Disease regions (De Jager et al., 2017; Prince et al., 2003).

References:

De Jager, C.A., Msemburi, W., Pepper, K., & Combrinck, M. (2017). Dementia Prevalence in a Rural Region of South Africa: A Cross-Sectional Community Study. Journal of Alzheimer’s Disease, 60(3), 1087–1096. https://doi.org/10.3233/JAD-170325

Prince, M, Acosta, D., Chiu, H., Scazufca, M., & Varghese, M. (2003). Dementia diagnosis in developing countries: a cross-cultural validation study. The Lancet, 361, 909–917. https://doi.org/10.1016/S0140-6736(03)12772-9