In some diseases classified as dementia, such as frontotemporal dementia, symptoms can start as early as age 50, states Mayo Clinic. Symptoms appear at different ages depending on the specific disease and patient. Symptoms of Alzheimer's disease often appear after age 60.
Dementia usually occurs when nerves in the brain become permanently damaged, according to Mayo Clinic. The damage may occur in different parts of the brain and can affect people differently. As of 2015, most types of dementia cannot be cured; however, doctors alleviate symptoms through the use of medicines such as cholinesterase inhibitors. Some doctors may also treat symptoms with several different therapies and altering the patient's environment to be less cluttered.