aging vs senescent

aging

adj
  • Becoming elderly. 

noun
  • The process of becoming older or more mature. 

  • The accumulation of damage to macromolecules, cells, tissues and organs with the passage of time; the progressing loss of health, mobility, vibrancy and body functionality, resulting in biological death. 

  • The deliberate process of making something (such as an antique) appear (or, in science fiction, become) older than it is. 

  • Wear; wear and tear. 

senescent

adj
  • Characteristic of old age. 

  • That ceases to divide. 

  • Growing old; decaying with the lapse of time. 

How often have the words aging and senescent occurred in a corpus of books? (source: Google Ngram Viewer )