Same way you prevent cuts and bruises from accumulating over the years: Repair and replacement. Your body doesn’t stay whole by preventing cuts from happening, but by effectively patching over them when they do. In principle there’s no reason this couldn’t be applied to DNA and oxidative damage. At least for DNA we know that mutation rates vary between organisms (as indeed do rates of aging), so it’s theoretically possible to lower the mutation rate.
Same way you prevent cuts and bruises from accumulating over the years: Repair and replacement. Your body doesn’t stay whole by preventing cuts from happening, but by effectively patching over them when they do. In principle there’s no reason this couldn’t be applied to DNA and oxidative damage. At least for DNA we know that mutation rates vary between organisms (as indeed do rates of aging), so it’s theoretically possible to lower the mutation rate.