I've co-authored a couple of tech books, published by Wrox and Apress. I don't think your age matters at all for this kind of thing, I think I got my first deal

I've co-authored a couple of tech books, published by Wrox and Apress. I don't think your age matters at all for this kind of thing, I think I got my first deal when I was your age. The biggest thing to understand that isn't obvious for a first-time author is that as soon as you sign the dotted line, you'll be on the publisher's schedule. They have to plan out when to release and sell your book months in advance. All of those chapter deadlines are also for the other people involved - tech reviewers, copy editors, production, etc. So if you run late, it squeezes them. I've done tech reviewing for a couple of programming books, and when the author gets behind, the editor pushes the tech reviewer to get the chapter turned around extremely quickly. Guess what that can do to the quality of your book! Another thing to know is that the "control" of your book is very strange, especially if its successful and the publisher wants 2nd and 3rd editions - check your contract, but they may have the right to assign another author to the book and release an update if you refuse to do the update. What this means in practice is that you end up having to do the update yourself whether you have the time scheduled or not to keep someone else from doing a crummy job updating your book.