The major (normal) cause of changes in facial features with aging is the resorption of bone (see this review by Mendelson & Wong. 2012).

Bone is typically built by osteocytes (derived from osteoblasts) and resorbed by osteoclasts. [Wikipedia]. When their action is in balance (homeostasis), the bone is stable. The activity of these cells is regulated by a number of secreted factors [see Bonewald, 2012].

With aging, the bone-building activity of osteocytes decreases, and there is a net decrease (resorption) of bone: the arrows in this figure (←) point to the major sites of resporption (from Mendelson & Wong).

When there is an increase in facial (and other) bones with age, it is generally caused by the aberrant production of growth hormone.

This is seen in the disease acromegaly, which is often due to the presence of a tumor of the pituitary gland, which leads to an increase in the secretion of growth hormone. Generally surgical removal of the tumor halts bone growth (and other effects).

One of the reasons that doctors often want to take pictures of their patients over time is so that such abnormal changes in facial features can be more easily recognized and tests for growth factor levels can be used for diagnosis.