The interactions between molecular damage in cells, repair system activity, the generation of reactive oxygen species (ROS) in mitochondria capable of causing damage, and individual or species longevity are far from simple. The free radical theory of aging and its variants were early and in hindsight overly simplistic views based on the observation that the presence of ROS and their signs of their damage increase with age.
Read the entire article here: https://www.fightaging.org/archives/2016/03/increased-generation-of-mitochondrial-reactive-oxygen-species-tends-to-slow-aging-in-laboratory-species.php