The Collaborative International Dictionary of English v.0.48:

ageing \ageing\ n.
   same as aging.

   Syn: ripening, aging, mellowing
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

ageing \ageing\ adj.
   1. having lived for a relatively long (or a specified) time;
      not young; -- used especially of persons. Opposite of
      young.

   Syn: aging, senescent, old.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Aging \Ag"ing\, n.
   the process by which objects or materials acquire desirable
   qualities by being left undisturbed for some time under
   specific conditions. It is used mostly for foods snd
   beverages, but also for other materials. [Also spelled
   ageing.]
   [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

ageing
    adj 1: growing old [syn: aging, ageing, senescent]
    n 1: acquiring desirable qualities by being left undisturbed for
         some time [syn: ripening, aging, ageing]
    2: the organic process of growing older and showing the effects
       of increasing age [syn: aging, ageing, senescence]