In a word:
Finally, a chance to download my bullshit onto a young, impressionable mind.
Here are the things you didn't realize you needed to worry about, but that you should be terrified of, in no meaningful order:
Television does rot your brain. Your brain is highly adaptive, especially when you're young; If you don't use it for difficult, complex problem-solving, your brain function will deteriorate. Use it or lose it. The medical term for this is Alzheimers. If you ignore this advice you'll be a much happier person, and I hope you do. Because if you try and stop TV/video games, you'll quickly realize that you cant. They are just as addictive as heroin. This is fine when you're in high school and you have friends, but just wait until you move out of town for your first job, and video games become your everything.
If you don't make at least six figures, you will be looked down upon as a lower-class citizen by others. I'm not saying that I'll be one of them, but you probably will. Aim for a career that accomplishes this, it's the reason that doctors/lawyers are such a mom meme. Or don't, and suffer crippling insecurity, your call.
Did your grandfather remarry later in life to ease the loneliness of idly waiting for death in a nursing home? Do you love your adopted grandmother? Just wait until your grandfather dies and she inherits all his money. She's going to leave it to her biological children and you're not going to see any of it. Everything that a man you knew and loved is going to be stolen by the woman that he trusted enough to marry. The major key here is that you should be self-sufficient and expect to inherit nothing, that way you'll never be disappointed.
You're never going to fuck the pretty girl, unless you're prepared to do morally questionable things to win her attention. The key word here is attention, not affection. Every girl has a price. Or maybe you want the pretty girl to fuck you because she loves you? I like your style. Either become sociable and flirtacious (difficult), or sell her drugs (easy). As a corollary, every pretty girl you know will eventually fuck on camera for drugs. So you could just wait until that happens and catch her on cams.com.
When I was your age, I couldn't wait to live on my own. My vision of adult life was being able to buy and drink Hawaiian Punch whenever I wanted. But I don't want Hawaiian Punch any more, I just want the loneliness to stop. It's a gaping void that you can only fill with so much food. Antidepressants are a plot to keep the populace satiated, and schizophrenia is just a symptom of an unfortunate condition called "knowing too much".
Livestock actually enjoy being eaten. So who is working for who?
One final note: there are a lot of idiots out there in the world. Not all people who give you advice are idiots, but invariably, all idiots love giving advice.
Good luck kid, you'll need it.