A 65-year-old man presents to his primary care physician with complaints of frequent urination, weak urine stream, and nocturia (waking up at night to urinate) for the past six months. He has no family history of cancer but is concerned because a friend was recently diagnosed with prostate cancer. His physical exam reveals a firm, nodular prostate on digital rectal examination (DRE). What is the most significant risk factor for developing prostate cancer in this patient?
