(1) The period that has elapsed since birth. (2) One of the periods into which human life is divided, distinguished by physical evolution, equilibrium, and involution; e.g., the seven ages of humankind are infancy, childhood, adolescence, young adulthood, middle life, senescence, and senility. (3) To grow old; to gradually develop changes in structure that are not due to preventable disease or trauma and that are associated with decreased functional capacity and an increased probability of death. (4) To artificially induce an appearance that is characteristic of one who has lived long or of a thing that has existed for a long time. (5) In dentistry materials science, the treatment of a material to stabilize or strengthen it by causing a coherent precipitate to form. A coherent precipitate is particle formation caused by clustering of atoms of one type as part of a lattice consisting of more than one atom type. [F. âge, L. aetas]