Most likely blackheads if they are on the underside close to where the hair growth starts. If you manscape, razor rash can cause that too.
If these are all over your shaft, top, sides, near the head, you should make an appointment with your doctor. At 20, it is most likely nothing serious.
Blackheads are caused by skin cells shedding during rough handling, rubbing against cloth, etc, and then clogging up pores. Very common. Even a zit or two is not unheard of; make sure Mr Happy and his two buds get soap time too.