Answer:
Chronic diseases.
Explanation:
Chronic diseases are those which persist for a long time and it is very rare at the beginning of adulthood.
A person having chronic disease can't easily find that he is suffering from that until he would get the major symptoms because it can be hidden by other activities and people will think they are completely free from chronic diseases.
In the last age of adulthood, many people suffer from this disease. Some examples of chronic diseases are heart attack, cancer, diabetes, stroke, etc.
