Background and Problem <p>Declining testosterone levels in aging men represent a growing clinical concern, with late-onset hypogonadism (LOH) affecting an estimated 20–30% of men over 60 years. The principal cellular basis for this decline is progressive impairment of Leydig cells, the primary source of testicular testosterone. Age-related Leydig cell dysfunction leads to reduced fertility, endocrine dysregulation, and associated systemic consequences including metabolic and musculoskeletal morbidity.</p> Mechanisms <p>Oxidative stress is now recognized as a central driver of Leydig cell aging. Excessive reactive oxygen species (ROS), arising from mitochondrial electron transport chain dysfunction, NADPH oxidase activity, endoplasmic reticulum (ER) stress, and chronic low-grade inflammation, disrupt redox homeostasis. This ROS overload impairs luteinizing hormone (LH) signaling, damages key steroidogenic proteins including the steroidogenic acute regulatory (StAR) protein and cytochrome P450 enzymes and triggers cellular senescence and apoptosis. Concurrently, the efficiency of endogenous antioxidant defense systems superoxide dismutases (SODs), catalase, glutathione peroxidases (GPxs), and the thioredoxin/peroxiredoxin network declines with age, amplifying oxidative damage within the testicular microenvironment.</p> Consequences <p>The convergence of increased ROS production and diminished antioxidant capacity impairs mitochondrial integrity, reduces steroidogenic enzyme activity, and accelerates Leydig cell senescence, collectively resulting in decreased testosterone biosynthesis. This contributes to the clinical manifestation of LOH, with downstream effects on spermatogenesis, bone density, muscle mass, metabolic health, and quality of life.</p> Interventions <p>Experimental and transgenic models demonstrate that overexpression of antioxidant enzymes can attenuate oxidative damage and preserve steroidogenic capacity. Pharmacological agents including melatonin, resveratrol, quercetin, coenzyme Q10, and N-acetylcysteine along with metabolic and lifestyle interventions such as moderate physical exercise, caloric restriction, and optimized micronutrient intake, enhance endogenous antioxidant pathways in preclinical settings. While robust human clinical trial data remains limited, these findings provide a mechanistic basis for translational investigation.</p> Conclusions <p>Antioxidant-based strategies represent potentially promising, mechanistically grounded approaches to preserving male reproductive endocrine function during aging. Future priorities include well-designed randomized controlled trials in humans, development of validated Leydig cell aging models, and multi-omics integration to identify precise therapeutic targets and biomarkers of steroidogenic decline.</p>