I found your website very interesting and cognitive! However, something occurred very recently to me, that I couldn't find anything about on the Internet, that is why I decided to ask you.
The thing is: my voice is starting to crack again. The key word here is "again" because I am already 16 years old, and if I filled out everything correctly, I am 4.5 on the Tanner scale. The last time my voice broke was at the age of 12 or 13. I remember these times very well because of the things I had to experience. I play the guitar, so voice is kind of important to me. After a couple of years, it seemed to me that my voice stopped cracking, and it was absolutely fine. I was happy with it. Now I am 16, and I started to experience the same voice breaking symptoms. When reading out loud in class, when singing, or just when laughing, my voice started to squeak and crack again. Thus, my questions are: When will my voice be done developing already? Is this normal to experience two voice breaks in your lifetime?
Voice breaking occurs when your vocal cords get longer, which results in you having a deeper and more manly voice. The difficulty is that the brain has to re-tune its knowledge of how tense to keep the vocal cords to produce the desired pitch because it is dealing with longer cords. When you are able to focus on it, it pretty much words well, but when your mind is on other things, brain gets the tension wrong and the voice squeaks and cracks.
While we would like to think of the development of the body as a smooth and gradual series of events, in reality it is a series of starts and stops. There just isn't enough energy for everything to develop at the same time, so different regions experience spurts at different times. Typically the voice box enlarges the most in stage 4, but it can start its changes earlier.
It sounds like that when you were in stage 2, your vocal chords got longer and your voice deepened. In musical terms, you probably went from a soprano range down to a tenor range. Now that you are in stage 4, your voice box is growing again, taking your voice down to a baritone or bass range. There is nothing wrong with it, the change in range, over all, was so dramatic that your body is taking it in a series of steps instead of all at once.