the process of growing old:the external signs of ageing
the process of change in the properties of a material occurring over a period, either spontaneously or through deliberate action:the judicious use of oak ageing means the wines are capable of being confused with the great French Chardonnays
adjective
(of a person) growing old; elderly:an ageing population
(of a thing) reaching the end of useful life:the world’s ageing fleet of oil tankers