Prostate cancer is common in older men, yet mechanisms linking aging to tumor progression remain incompletely defined. Beyond genetic alterations, aging reshapes the prostate microenvironment through cellular senescence, chronic low-grade inflammation, immune dysfunction, stromal remodeling, metabolic stress, and impaired tissue repair, collectively promoting inflammaging. This persistent inflammatory state may create a permissive niche for tumor initiation, progression, immune evasion, and treatment resistance. Senescent epithelial and stromal cells release cytokines, chemokines, growth factors, matrix-remodeling enzymes, and extracellular vesicles through the senescence-associated secretory phenotype (SASP). In parallel, immune aging alters T-cell subsets, myeloid cells, macrophages, and anti-tumor surveillance. This review summarizes how SASP programs, Th17/Treg imbalance, IL-17/IL-23 signaling, myeloid remodeling, stromal aging, metabolic stress, and immune–stromal–epithelial crosstalk shape prostate cancer biology. We further discuss therapeutic implications, including cytokine modulation, senescence-directed therapy, metabolic intervention, and biomarker-guided strategies. This review highlights key knowledge gaps and proposes a framework for age-aware prostate cancer research, biomarker development, and therapeutic strategies.