Get a good education, maybe engineering. Get a good job so you can afford cars and work on them in your spare time. Find a woman who supports your car fix.
Lots of good suggestions here Sam. Ask around to uncles, cousins, friends (and friends' parents) to see if any of them share your passion. Go to car shows and talk to the people there. Don't be shy. Show an interest and car folks will most often go out of their way to help you out.
And I'd like to add something from my own experience working with my grandson when he was about your age. It might seem strange, but working with your hands is just as much a mental exercise as a physical one. Patience and a cool head will help lead you to success while rushing into things and losing your temper when they go bad will only leave you frustrated. In any of the activities that have been suggested take your time. Plan what you need to do. Assess your abilities and resources before you begin and fill in the holes (information, skill, tools). Proceed slowly and methodically. When you hit a roadblock (and we ALL hit roadblocks) stop, step back, take a couple of deep breaths and ask yourself exactly what happened and why. Then you can plan a path to fixing it. Broken bolts and parts that don't fit aren't a reason for anger. Use what you've learned along the way to help you out of your current situation and then add this new knowledge to your data bank. The more you know, the more you can do. And the confidence you'll build will help you in all aspects of your life. There's a wonderful satisfaction that comes from being able to say "I did that".
All the best of luck to you and always remember Wells' law of engine size: If it matters what gear you're in, the engine is too small.
Learn to get organized and document everything no matter what you do. Just basic documentation like tagging and bagging will go a long way to help make any project successful. Tag all parts, nuts, bolts and screws. Draw a diagram showing where each nut was so you can put it back together the same way.
I agree with all of the suggestions and recommendations that everyone has made up to this point. If you don't have a person that you can mentor to put a wrench to an actual car I have a couple of suggestions. 1) Ask around at a garage to see you can job shadow them for a a few days until they get to know you. 2) If you have a car that you can work on, while you are putting a wrench to the car... use your cell phone to video what you are doing so that you can figure out how to put it back together. 3) I think it is very important to learn how to detail a car. There are a number of videos on You Tube that can help you. Just remember that you are starting out. Ask a bunch of questions and then go out to find the answer. I was blessed to have a Dad and Grandfather that helped me learn to work on vehicles. Don't let it intimidate you.
Start small. Start with broken lawn mowers and weed eaters. Try fixing those things and see if you like messing with the mechanics of engines. If you hate getting dirty, then you've got your answer. If you don't mind a constant grime in the cracks and crevices of your fingers, you may have a future playing in the car world.
One other suggestion... When it comes time to get your first car, get the best condition car you can possibly afford, even if it's not the car you want to drive. It's far better to drive around in a beat up Toyota than to have a broken MGB that you can't afford to fix sitting in your driveway.
I would suggest getting a high production number, common but fun vehicle- Camaro or Monte Carlo SS from the 1980's. GM/ Ford v-8 pickup from the late 80's onward (short bed), as new as budget allows Ford Mustang (or go for a 1987-1993 Fox 5.0). Reason being there is tons of info on these types of cars and parts are readily available. 98-2002 Camaro/ Firebird LS/v-8 would be sweet. Older sporty toyota/ lexus, honda/ acura.
Airbags would be a bonus of some of the newer models.
I got a beater 1988 Chevy S-10 4 cylinder 5 speed king cab. No power and not a hot rod, but it was MINE!
I'm actually 14 myself, and some of the best advice I can offer is to just dive into mechanical projects. Depending on what you're willing to spend, fixing an old go kart can teach you a LOT about cars, while also giving you something fun to drive. I started with almost no mechanical experience and now I'm swapping out and custom modifying cams, shaving heads, putting on aftermarket carburetors, and even swapping out connecting rods!
Another great piece of advice other people have offered is to find someone who will teach you. Car clubs and online forums are fantastic resources for this.
And one more thing: READ! Read all the manuals you can about what you want to do! Youtube videos are also good to get you "fired up" and going, plus there are a TON of Youtube tutorials.
Good luck, and welcome to the hobby!
Agree with the YouTube videos, blog posts on your favorite sites, etc.
Buy yourself a decent set of basic tools to start with, something with a warranty. You don't need Mac or Snap-on yet. You'll get as many opinions on tools as you ask for. Kobalt (Lowe's) is a decent set with a warranty on most items; but there are others, too. You can look on the Nextdoor app, FB marketplace, and local Craig's list for a used set, too. Good Luck!
Take what ever cars you like and seek out owners of them at car shows, blogs and car clubs. Hooking up with enthusiasts is one of the best ways to enter a hobby on the ground floor and rise quickly through osmosis via their shared knowledge. People like these in the hobby will go out of their way to share the highs (and lows) from the years of cutting their teeth just like you are about to embark upon. Remember, they started out once upon a time like you are now and learning from their mistakes saves you from committing them yourself. Add to that if you are lucky enough, you could maybe apprentice with them and even work on your car in their shop with their expertise along side you. This is how I got into my first bike - 1975 Harley FLH basket case. I got hooked up with a Harley mechanic. I told him I wanted to do as much work as possible so I ''knew'' my bike inside and out instead of just owning and riding it. Between him and all his buddies, there was no question too dumb to ask. Their love of the hobby was shared willingly with me. And the bonus was when we dropped the bike off the lift the first time. He said it was the prettiest bike even to come out of his shop! The 2nd bit of advise I ever got was to buy the most amount of car you can afford. What that means is put more into the highest level of that car you can buy so you have less needed funds to come up with to fix what can be avoided in a car of better shape. This is proven best once you get into buying a hot rod someone else built but then sells. More often than not, they never recoup the money (and more importantly the labor!) they put into it.