Your first book is going to suck
Is it okay to publish your first book at a young age?

Short answer: Yes, you can. Even now.
Long answer: Very few authors ever really make it with their very first drafts. While I’m no published author, this is what I do know about publishing a book.
It’s okay to publish a book at any age if it’s a good book (or at least, good enough). If you can’t publish at say age 13, you can try again at age 18 or age 23.
As a teen, you can self-publish your book as an e-book, but you are more likely to be struck by lightning than get it published as a conventional book without a whole lot of work first.
The thing is, your first book is going to suck. No matter what you’ve heard, very few writers have had their first book accepted at a tender age as the first draft, without a lot of editing and revision first.
Book deals take a lot of time. If you are writing in a genre that still accepts unsolicited manuscripts, virtually every first author that I have ever heard of, has said it took at least, a year before they heard from the publisher about accepting their book. And then they went through at least another year of revisions and edits, and then it was another year before it was actually published.
Chances are, the books you are seeing on the shelves this month were probably turned in this time last year and may have been turned in two or three years ago. If you are not writing in a genre that accepts unsolicited manuscripts, it’s going to take still longer, because you’ll have to find an agent first.
In addition, you need to ask yourself three hard questions.
How badly do you want this?
Your first book, professionally speaking, is going to suck, and I can tell you that without even seeing it. Why? For the same reason that a 14-year-old who has just begun learning to play the bassoon sucks. Probably three to four times as much work as you put into writing your book will go into revising and polishing it. So how badly do you want this?
Can you take criticism for what it is, correction and something to help, and not an attack on you?
One of the things a professional writer learns early and takes to heart is that a professional critique, no matter how harsh, is not a personal attack. And no matter how much you love that sentence, that paragraph, that chapter, if a pro editor or pro author says it’s crap, well, it’s crap. What’s more, your book stopped being “yours” the second you let someone else read it. Let it go, Eli. It’s not your heart, it’s not your child, it’s something you made, and if you made it badly, you need to understand this is true, and why, and how, in order to understand how to fix it or how to write the next one better. If you can’t take criticism that is going to rip your book to shreds, don’t go into this. Because if you think editors are bad, hoo boy, wait until you see what your fellow teens who are not your friends are going to say about it. So can you handle harsh criticism?
What’s more, your book stopped being “yours” the second you let someone else read it. Let it go, Eli!
Are you willing to work at a career and writing at the same time?
Here’s the cold, hard truth. Only 10% of the membership of the Science Fiction and Fantasy Writers of America make a living at writing, and of that 10%, half are also into things like journalism and technical writing, and of that 10%, 9% are just making an ordinary living (we call this being “high midlist” writers). The same is true in every other genre — probably things are even harder in mainstream writing (The Fault In Our Stars or About a Boy would be considered “mainstream”). What this means is, like it or not, you are going to have to have a day job, and write in your spare time. Which means, like it or not, like everyone else in your class, you need to start thinking and planning for what you are going to be doing for the rest of your life besides writing. Can you do that? If the answer to all of those things is “yes,” then you’re ready for a long, difficult, but rewarding, time. If the answer to any of them is “no” — then consider writing for yourself, for your friends, as a rewarding hobby.