food. They don't do exercise. They have all kind of medical issues when they get to middle age.  Most people I know have some sort of medical problems. Even they look healthy, but most of them are at borderline to develop heart diseases, diabetes and others. They don't understand how to stop the progression to chronic diseases. Even without the COVID, their prognosis is grim. With the virus, it just speed up the development.

Of course, as people getting older and older, immunity system will become weaker and weaker, Lots of body functions are dramatically decrease e.g. endocrine secretions, insulin, beta cells,...  It is hard to fight the virus without a strong immunity system and a healthy body. The virus is very taxing on the body. That is why people should be extra careful at age 65+. They should have a much much healthy diet and maintain an active healthy lifestyle. Some doctors only eat one or two meals a day to keep their body strong and slim. Have extra fat tissue can decrease immunity system, insulin sensitivivity among others. Drink tea and exercise will help improve the immunity system. In some place in China and some islands in Greece many people there live to age 100+ because they drink tea and climb mountains to tend their gardens.