The thymus is a small, butterfly-shaped gland located in the upper chest, just behind the sternum. It plays a crucial role in the immune system, particularly during childhood and adolescence. The thymus is responsible for the maturation of T cells, a type of white blood cell that helps the body fight infections and diseases. As a person ages, the thymus gradually shrinks and becomes less active, a process known as thymic involution. This reduction in size and function can impact the immune response, making older individuals more susceptible to infections. Despite its decline, the thymus remains an essential organ for developing a robust immune system early in life.