Mitochondria generate adenosine 5'-triphosphate (ATP) and are a source of potentially toxic reactive oxygen species (ROS). It has been suggested that the gradual mitochondrial dysfunction that is observed to accompany aging could in fact be causal to the aging process. Reviewed findings suggest that age-dependent mitochondrial dysfunction is not sufficient to limit life span. Furthermore, mitochondrial ROS are not always deleterious and can even stimulate pro-longevity pathways. Thus, mitochondrial dysfunction plays a complex role in regulating longevity.

Reference:

Ying Wang, Siegfried Hekimi "Mitochondrial dysfunction and longevity in animals: Untangling the knot", Science 04 Dec 2015: Vol. 350, Issue 6265, pp. 1204-1207