Unless you are a dog your testicles already 'dropped' when you were born. You do want to avoid any injury to your penis or testicles. Start wearing a jockstrap for protection if you really need to. Don't wear tight underwear to protect your gems. Boxers are better. Your body grows until you're 18. And, remember, 2/3 of the top part of vagina doesn't have any sensation, so as long as your penis is 3 inches you'll do just fine. Most women prefer girth not length anyway. Take care