I applaud the idea, but I think this book needs some serious work before it is suitable for your intended audience.

For example, in Section 1.1 you explain how to go about solving the equation x^2 - 4 = 45, a topic which (I would venture) most 16 year olds should be comfortable with.

Then in Section 1.2 you, out of nowhere, introduce set-theoretical ideas and notation. Even seemingly innocent notation like

    {0, 1, 2, 3, ...}

to denote the natural numbers can be confusing for someone who hasn't seen it before. In this case it's clear that the dots are supposed to indicate "continue in the obvious way". But then you write

    Q = { -1.5, 1/3, 22/7, 0.125, ... }

in which the dots, presumably, mean something different. Then, at the bottom of the page, you suddenly start using the notation "∈" to denote set membership, as in

    if x,y ∈ N, then (x+y) ∈ N.

First, what does this weird "∈" symbol mean? Second, what does it mean to write "x,y ∈ N"? Is that x∈N and y∈N? Or is it some special object "x,y" that is ∈N? Or is it two statements, "x" on its own, and "y∈N"?

The next couple of paragraphs contain both historical and mathematical inaccuracies (can you really always divide two rational numbers to get another rational number?). I'll stop there.

Like I say, I applaud what you're trying to do. I think you have a noble aim. But if the preview is anything to go by, your textbook in its current form is falling short of that aim.