Ok, I have this question: Boys try to be cool saying in school that they masturbate. They are all 13 years of age. When you masturbate does this affect your period of change?
Boys will talk about masturbation because it is "proof" that they are growing up. It is just an extension of what used to happen in younger years when kids compared each other's height or age: "I'm older than you are" or "I'm bigger than you are," implying "You better do what I say." Ejaculating semen means that they have the potential to father children, but it doesn't mean they are adults. They only have reached one stage on a long road to adulthood.
On average, many males begin to be able to ejaculate at the age of thirteen. That is why you are hearing a lot about it now. Of course, some will start sooner and others later, but these boys rarely talk about it because it marks them as being different from the rest. During the teenage years there is a strong urge to be like your peers.
But does it effect your growth in any way? No. Ejaculating involves a series of organs in your body. It didn't happen earlier because the organs had not yet matured to the point of being able to produce semen. The fact that semen is being produced just states where a male is in his adolescent growth. It doesn't alter his growth. (Such would be like saying that urinating will change how you grow.)
See the end of chapter 2, "Your Body" for more information about masturbation.