Very Rare. Prostate cancer is the disease of elderly.
Uncommon. Never met a patient like this, although we don't usually check on them, either. However, i've never met someone who died of prostate cancer this young.
Very very rare. Primary cancer of the prostate is rarely ever diagnosed in anyone under the age of forty. While we do not screen these patients I have never read of a case of adenocarcinoma of the prostate in the teenage population.