I am a 14-year-old boy and I cannot speak in the middle of my voice.
This will change very soon. You are at an age where your vocal cords are developing another layer of skin cells and the hormonal changes are also causing the cords to grow. Speak gently in the low voice and it will be more likely to sound. Then try to slide that easy sound up toward the middle, like you are making a little siren. If the voice goes to the middle, you can then try to speak a little there, but very gently. Just take it easy and relax, don’t force or push, and the change will be accomplished before you know it. Meanwhile, trust that you are a wonderful person and simply say what you need to say with spirit and heart.