I have two younger sisters.
One has been divorced and has three kids with three different fathers. I think there was a time that I stopped hanging out with her and I think that might have been it.
The youngest one, I made sure to make sure that she had a steady diet of Super Nintendo early on, I bought extra copies of games to make sure she had a copy, it also helps that she completely thought her older sister was obnoxious for getting married young. That, and lots of anime, documentaries, sci fi, video games, and books have kept her from getting into trouble at college. Instead of going out dancing or drinking, she stays in her dorm and calls me to talk about The Legend of Korra, Doctor Who, Sherlock, or whatever awesome animal she's discovered on the internet. I made sure that she reads things like murderpedia, The Smoking Gun, and others. There was a point a few weeks back where we were sending photos back and forth of awesome spiders. (Peacock Spiders are the best spiders.)
I would be surprised if she ever decided to date or what not. But I also made sure that.. if she ever does.. she knows how to handle a gun, she knows basic self defense, I started doing this thing where she would enter a room and then tell me at least 20 ways to kill someone with the stuff in the room. It's not the most cheerful of games, but it should be something to think about. You know? When you enter a room, think about how to get out of that room quickly. Be aware of exits, items to use as weapons, and so much more.
But yeah. I was so nervous with that one because the middle sister ended up with early marriage and kids. BUT she never went down the horrible path of bad drug addiction. Or alcoholism. Actually, that's probably because we had wine in the house and stuff for cooking. We never treated alcohol as a huge "don't drink it" thing. It was always just "Well, it's here if you want to drink some, but keep in mind that it impairs you. There's a trade off for it. A little in the morning is healthy, too much of it will make you act like an idiot." The middle sister smoked for a while until eCigs became an option. Personally, we encourage the use of eCigs over regular cigarettes. It's either that or chewing gum and chewing gum is rude.