This topic is probably one of the most discussed issues on Catholic Answers, and inspired by another thread that I commented on, I wanted to make a separate thread distinguishing this issue for itself.
Firstly, for a good, Catholic understanding of this issue, I encourage you to watch this video:
Sin, whatever it might contain (or rather, lack) is not that of desiring too much, but rather of desiring that which is not enough. We are called to have desires and to have those desires fulfilled, but all fulfillment, in order to be fulfilling, must come from God. Therefore:
"We fall into sin when we are ignorant of the motives beneath the desires. Consider this way of understanding personal sin: We sin, not because we are in touch with our desires but precisely because we are NOT in touch with them!" ~Catholic Update to Vocations
With sexuality, we are given a strong desires (biologically and hormonally), especially as males (the same stands for some females too), but what seems paradoxical, but actually isn't, is that we ought to channel those powerful desires (sexual or not) into something better, something more pleasurable: God. What this does, is build fulfillment and strength. It's about seeking sexuality better. As a famous quote on the evils of pornography goes, it is not that pornography shows too much of a person, but rather, too little.
"To love is to will the good of the other."
Also, let me state, that from what I can remember in history/bible class at a Jesuit school, that Jewish marriage was often conceded at a young age through agricultural families. In our society today, not marrying young is a choice and holds consequences. There was no 18 or older imposition back then, and some young men married at early ages. In our age, we might choose University and a job first, but that action holds a consequence. What is most important is that Love's end meets in Providence.
Regardless, try watching the video above by Father Robert Barron. It probably will help more than my words.
So why did God give us such powerful hormones and such a wonderful sexuality?
To know God better, through proper context. That and self-sacrifice.