Hey!
Elders have several medical issues, such as arthritis, cancer, heart disease,diabetes. There are even mental ones such as dementia, or Alzheimer's disease. However, some of them go unknown like cancer, until tests are ran or you have skin cancer and you develop outside lumps. However, mental illnesses are usually simple to diagnose. Sometimes, they might forgot your name, or where they are. They just stare at nothing, or they talk to themselves and wander around. People who age do forget more things, but they are usually alert and aware of their surroundings.
Hope this help!