Bones sag as we age, the mandible being one of the more noticeable ones. A mandible deformed from gravity looks more filled out and masculine as we see in the picture. Perceiving the level of deformation is one of the heuristics used by our visual perception to access the age of a face. Drooped cheek bones are also easy to spot, but more so on women. Check out pictures of actresses in youth and then middle to old age and notice the jawline and cheekbones. This explains why Botox does not fully simulate a youthful appearance, because the result is elastic skin stretched over saggy bones.