The american cancer society recommends:
50 years for men at average risk.
45 years for men at higher risk (african american men, men with father or brother diagnosed with prostate cancer
before age 65 years).
40 years for men at highest risk (multiple fam members diagnosed with prostate cancer by age 65).
But i recommend every man start at age 40. The most aggressive cancers start younger.
Answer assisted by David Miller, Medical Student