To summarize it from the American Cancer Society 2016:
Age 50 for men who are at average risk of prostate cancer and are expected to live at least 10 more years.
Age 45 for men at high risk of developing prostate cancer. This includes African Americans and men who have a first-degree relative (father, brother, or son) diagnosed with prostate cancer at an early age (younger than age 65).
Age 40 for men at even higher risk (those with more than one first-degree relative who had prostate cancer at an early age).
After this discussion, men who want to be screened should be tested with the prostate-specific antigen (PSA) blood test. The digital rectal exam (DRE) may also be done as a part of screening.