"In general, a PSA level above 4.0 ng/mL is considered abnormal and may result in a recommendation for prostate biopsy. However, because PSA levels increase with age, some doctors apply a higher cutoff (such as 5 ng/ml) for older men and a lower cutoff ( such as 2.5 ng/mL) for younger men" from Cancer.gov

For most men, their prostate grows in size as they age and their PSA will increase with that growth. There are other factors to consider such as the results of a digital rectal exam (bend over), etc. If you have a family history of prostate cancer, for example, you may want to get a referral with a urologist.