Dementia caused by Huntington’s disease may begin as early as age 30, while frontotemporal dementia, a condition linked to nerve cell degeneration in the frontal and temporal brain lobes, may manifest as early as age 40, according to MedicineNet. Dementia caused by corticobasal degeneration can occur beginning at age 60.
The type of dementia or its cause often determines onset, notes MedicineNet. For example, Alzheimer’s disease, a disease characterized by dementia, is the most common cause in people age 65 and older, but it can occur at earlier ages. HIV-associated dementia can occur in anyone of any age infected with HIV.