Answer: Many boys begin to have nocturnal emissions ("wet dreams") when they start puberty, or soon thereafter (usually around 12-14). Wet dreams (ejaculating when you're asleep) is the body's way of releasing "built-up" semen. How often this happens depends, but it's usually not often -- if at all -- if/when boys regularly masturbate. Masturbation releases the semen that would otherwise "build up."