Unfortunately this creates a paradox. Free radicals are the signal that you need more mitochondria. When they are released they damage the DNA in the mitochondria you already have. The only way to correct the balance is for the mitochondria to divide, making more of themselves, and as an unfortunate consequence, the damage done by the free radicals gets magnified. Eventually, there are more mutated mitochondria inside your cells than clean ones, and the whole operation of the cell becomes degraded because of the extra resources this consumes.
As the mitochondria decline in efficiency, the cell will shift across the spectrum of genes it can express, to devote more resources to mitochondria recycling. This reduces its effectiveness as part of a functioning organ. (Stem cells and heart cells do not divide their mitochondria, and therefore are not directly under the influence of this cycle, but they can still suffer from the decline in other organs.) Each cell also has a feedback loop of signals inside it, designed to detect this degradation. When a cell in your body realizes it has dropped below a reasonable efficiency level, it commits suicide, removing itself and its damaged mitochondria from your collective internal gene pool.
Here's what this means for you, on a human scale: When you pass through a cycle of stress, part of you dies off while the rest of you decides to repopulate, spreading slightly less efficient mitochondria throughout your tissues, resulting in a subtly decreased energy level. You really begin to notice it in middle age.
This effectively cannot be reversed, because you can only work with the genetic supply of mitochondria that you have. Your best hope for renewed health is to maintain a higher set-point for energy capacity, via a higher standing population of your current mitochondria, so that when you are pressed into other capacity modes - higher stress modes - you do not logjam your energy supply chain and create damaging free-radical elements inside cells.
In other words, sufficient sleep, complete nutrition, and consistent aerobic exercise places your body into its most long-lasting mode. It delays the onset of virtually ALL late-life diseases.
This may seem like common knowledge, but now you understand why it is so... And why there is absolutely no product, service, or diet that can turn back the clock. Your very best outcome is to slow it down.