The causes of dementia in the elderly can be varied, with many diseases such as Alzheimer's disease, Parkinson's disease, and vascular dementia, all leading to senile dementia. Therefore, how long one lives may require specific analysis.

If the dementia is due to cerebrovascular factors, the lifespan of the individual may be closely related to the primary disease, i.e., cerebrovascular disease. Dementia caused by Alzheimer's disease progresses with the disease and affects the patient's lifespan. In its advanced stages, when the patient can no longer take care of themselves, complications such as lung infections can further impact their lifespan.

There are also other factors, which need to be assessed based on the evaluation of the disease.