I like the way Mark Driscoll answered this question. To motivate them to grow up so they can take a wife. Nearly every man wants to have sex and has a strong sexual desire. Those desires should motivate him to study hard, walk faithfully with God, compete courageously in life, leave home and pursue a career where he can support himself and a family. Then, when God blesses him by bringing the woman he should marry into his life, he can marry her and be a blessing to her, not a burden on her.

This strong sex drive should motivate boys to grow into men. Testosterone should not focus a man toward pornography and fornication but focus him toward courage, hard work, maturity and marriage. Letting your testosterone lead you into promiscuity where you take a woman before her wedding night and become intimate with her is stealing from her husband intimacies that should be his alone. Premarital sex is a boy acting in childishness, not a man acting in godliness, patience, discipline, and maturity. If that is you, it needs to be repented of.

Let your fountain be blessed, and rejoice in the wife of your youth, a lovely deer, a graceful doe. Let her breasts fill you at all times with delight; be intoxicated always in her love. Why should you be intoxicated, my son, with a forbidden woman and embrace the bosom of an adulteress? For a man’s ways are before the eyes of the Lord, and he ponders all his paths. The iniquities of the wicked ensnare him, and he is held fast in the cords of his sin. He dies for lack of discipline, and because of his great folly he is led astray. Proverbs 5:18–23 (ESV)

Portions in this post taken from Mark Driscoll Sermon Archive