Young boys cannot ejaculate. A boy's first ejaculation usually happens about one year after he begins puberty, which is when his body starts changing into a man's body. Most boys go through puberty in their teens. The first time a boy ejaculates usually happens when he is asleep. This is called a nocturnal emission (which means "an emission happening at night") or a wet dream. It happens without the boy's control, often when he is having a dream about sex. Scientists believe that wet dreams are the body's way of removing too much semen. When a boy begins masturbating, wet dreams usually stop happening.