Let's work from the original. The OT law of the 10 commandments included "Thou shalt not commit adultery". Now, God doesn't simply give laws willy-nilly . Why did He give that law???? Answer --to preserve the marriage, the family unit, that it wouldn't be a threat by an outsider coming into an illicit relationship between the married.
Move forward. Jesus is addressing the HEART of that law and how to guard it from committing an act that was a threat to MARRIAGE. So of course when single boys and girls grow up they will become awakened to sexual feeling (not sin), and they will feel attracted to certain opposite sex partners(not sin), and their mind will operate in sexual thought and desires (not sin). Masturbation is a normal practice that is self-nurturing and a way to deal with powerful hormones, ALL which is not sin because it is not placing in your heart the impetus to go out and commit adultery.