Clearly defined lower jawline and chin is a sign of youth. Besides that, it provides a clearly defined line of the face, separating it from the neck. At times, chin is not as visible as it should be due to genetics. The lower part of the jaw might not be well formed which makes the face look undefined with a noticeable double chin. With age, the edges of the lower jaw disappears due bone resorption, lowering the fat tissue of the face, sagginess of the skin, accumulation of double chin fat tissue etc. This makes noticing the line between the face and the neck quite difficult.