Dear Roger: Is 17 The Edge of The End Of Sanity?

What the hell is it about the age 17 and boys that causes all of them to seemingly lose their ever loving minds? My eldest son turned 17 in December and it has been nothing but drama and lunacy ever since. He is brilliant and gifted and can play just about any damn musical instrument he cares to pick up, teaches himself advanced computer programming and even fixes and rebuilds computers for the hell of it, can discuss and argue politics and religion with adults to the point that he is now a moderator on several posting sites because of his alleged maturity, yet, he freaking dropped out of high school.
Hes a good looking, intelligent, and when it comes to others; kind, young man, but he will torture his baby sister to tears for no apparent reason other than he for some reason thinks she is the favorite child and he has to balance the equation by being hateful to her.  He will be snide and mean and damn right cruel to her for days and then out of the blue tell her that her favorite boy is going to be on some tv show and set up the scheduler on tv so she wont miss it.  He curses my dog and makes dire threats towards his very life, but then he will sit and cuddle him for hours when Benny isn't feeling well after getting a shot. I would suspect him of being bi-polar, but hes been tested and talked to and evaluated and other than some issues related to what we all went through back in Arizona, he is perfectly,"Normal".
If that is normal, I am terrified because I have 2 more boys about to enter fully into their teen years and it is not a barrel of laughs, especially for a small, scrawny, single mom. Things have been better with my two friends around because they have become mentors of sorts to the boys and with a couple of male role models around everyone seems to be enjoying things a lot more. They tease my son about his,"Stick up the butt" mentality and make him actually participate in things like game night, and they make him socialize, and they tease him about all kinds of things that he needed teasing about. I know he has blown off time with his girlfriend to hang out with them and to spend game night around, and though I didn't realize it at the time, he really did want to go to Karaoke with us even though he never committed. Hes been kinder to my daughter as well, at least when they are around.
They are why I kind of have hope that my son will hopefully turn into a sort of sane human being once he navigates his teen years. Though I have seen examples of young men who just wallow in one disaster  after another, these guys seem to have their shit together and they are successful and fairly well adjusted and my son looks up to at least one of them, all my kids do.
We have adopted them into our rather odd family and they are here every night for dinner, we spend time together every day and they are going to the Spencer Bell Legacy concert with me in June. Its been great for us, and hopefully good for them. Having friends that I can socialize with and that my kids look up to and enjoy being around is an amazing thing, and if they can help my wayward son figure out his life, then all the better.  I have hopes that the influence of the two seemingly sane and normal men around will have a calming and stabilizing influence on my sons, especially my eldest, but I really don't know. I do know that when they are around his fits of temper and his bullying of all of us are stifled, and he gets called on his bullshit, but there are days I despair him ever turning into any kind of tolerable human being. Tonight is a perfect example, he is ensconced in his room, playing Assassins Creed on a flat screen tv that I pay for, on internet pay for, utilizing a set of sound dampening head phones that cut off all contact with the outside world, and woe be unto him who dares to interrupt him in his battles. He rages and screams at the little kids or even me, slamming things around and slamming doors to the point that the walls shake throwing a fit like a toddler denied a toy just because he was asked to tell me where he put my Iphone cord. There are times I want to just tell him to take the things he actually has bought himself and leave, that would be less than a backpacks full of things, yet he acts like he is the most put upon waif to ever walk the earth. He is not in school, he is not working, and getting him to do even the basic of household chores involves major cajoling. I don't know where I went wrong with him, other than to say I spoiled him like many Texas mothers tend to do their first born sons, and now I am paying the piper for it. I hate to say it but I am just counting down the months to him turning 18 and hoping with age comes wisdom, sanity, or maybe a realization that hes got it a lot better than he realized.