The gradual accumulation of cell damage plays a very important role in the origin of ageing. There are many sources of cellular damage, however, which ones are really responsible for ageing and which ones are inconsequential for ageing is a question that still lacks an answer.
The Oxidative Hypothesis of Ageing -- also known as the Free Radicals Hypothesis -- was put forward in 1956 by Denham Harman. Since then, the large majority of attempts to prove that oxidative damage is relevant for ageing have failed, including multiple clinical trials in humans with antioxidant compounds. For this reason, although the accumulation of oxidative damage with ageing is undisputed, most scientists believe that it is a minor, almost irrelevant, cause of ageing.