Hi, Joshua!  Thank you so much for those kind words.  I’m honored that you feel that way about my books!  Yes, you’re right, Gordon did start his publishing career early.  His first book was written at age 12 as an entry in a Scholastic contest, and it was published when he was 14.  You should look into the Scholastic Art and Writing Awards and think about submitting something.
But keep in mind, Gordon wrote that book about thirty-five years ago.  The world of children’s books has changed a lot since then.  Many more books, much more competitive.  So my first word of advice is to be patient.  If you love to write and you’re really excellent (both of which I am assuming with you) AND you continue writing, well, the sky is the limit.  Even if you don’t hit the jackpot right away, you will only get better and better.  Most currently published writers were excellent too at age eleven, but they were not publishable quite yet; they were WAY better as they got a bit older.  Writing well really does take time and practice.  It’s a craft, like sports or music.  An excellent 11-year-old cellist is not necessarily going to find a job with the New York Philharmonic; 11-year-old Derek Jeter would not have made the Yankees.  And that’s perfectly okay.  Life is long!
Here’s some advice I usually give people who are serious about writing books:
1. You have to want it more than anything else in the world. You have to be the kind of person who doesn’t settle for no.
2. Reading voraciously — all the time — is the single best training to become a writer.
3. It helps to be intensely curious about how your favorite authors make their work so good. What kind of words do they use? What kind of words do they leave out?
4. As I mentioned above, you need to practice. Writing gets better with constant work. Write some things for yourself, pieces that no one else sees. Also write stories that you show to people you respect — teachers, librarians, parents, siblings, other authors, etc. Listen to their feedback. Learn to recognize useful and useless feedback. Useful feedback is your best friend, even though it may feel painful.
5. You must collect ideas. Write them down. A pad or a writer’s notebook is great, but anything will do, even a receipt or a scrap of paper. Collect your ideas from conversations, things you observe in everyday life, dreams, other books and movies, etc. When you have a bunch of them, read them over and decide which is the best. Which one makes you the most excited? Start working on that one. If you like it, chances are your readers will too.
6. You need to recognize that the stakes in your story must be super-high. Even in stories about everyday life, there must be some dilemma that seems impossible to solve, something the readers will hang on to until the very end.
7. Regarding step 6, think hard about what you want to leave out of your story. That’s the thing that will pull your readers in.
8. Live life to the fullest. It’s easier to write compelling stories if you’ve experienced compelling events in your life.
9. Don’t worry about getting published right away. Almost no one is published at a super-young age, and that’s OK.
10. Did I say practice?
11. Practice.
And good luck to you.  Maybe someday, when you’re a published author, we’ll meet at some big conference.  Be sure to introduce yourself!