Synonyms for Ageing (same or very similar meaning)
WordNet sense 1 (acquiring desirable qualities by being left undisturbed for some time):
aging, ripeningWordNet sense 2 (the organic process of growing older and showing the effects of increasing age):
senescenceWordNet sense 3 (growing old):
senescentWordNet sense 4 ((used especially of persons) having lived for a relatively long time or attained a specific age):
oldFrom the ODE community, based on WordNetadd/edit