What does "age of onset" refer to in a health context?

In a health context, "age of onset" refers to the age at which a health issue arises or first presents itself. This concept is crucial because understanding when a condition begins can provide insights into its development, progression, and potential interventions. For instance, in chronic illnesses or developmental disorders, the age of onset can significantly influence prognosis and treatment strategies. Early detection may lead to more effective management, while late onset could indicate different underlying biological factors.

The other options, while related to health, do not accurately capture the definition of "age of onset." The age at which treatment begins pertains to therapeutic interventions rather than the emergence of the health issue itself. The age of the patient at diagnosis focuses on when a diagnosis occurs, which may not reflect when the condition actually originated. Similarly, the age when symptoms are most severe can vary widely among individuals, depending on various factors, and does not denote the initial point of onset.