Vibrating Objects produce sound:

Any object that vibrates, such as vocal cords, uvula, lips or even a piece of tissue, can produce a sound with a specific pitch based on the frequency of its vibration. 

 Voice:

The puberphonia voice is also produced by vibrating structures (vocal cords). The frequency at which the vocal cords vibrate determines the pitch of the voice. Puberphonia males have normal long, thicker vocal Cords, typically should have lower pitched voices (due to thicker and longer vocal cords) that vibrate slower. 

In puberphonia it creates a high pitched voice. Why?

Answer is UMAR.