Why my voice isn’t deep?

Each teen goes through puberty at a different stage of his life. During puberty the voice starts getting deeper as testosterone enlarges the larynx and vocal chords.

Low levels of testosterone can prevent a man from developing a deep voice. 

Emotions such as anxiety can make a voice high pitched. If you always experience anxiety around others then you might not be talking with your real voice. 

When a person speaks fast his voice can sound less deep. Speaking slowly can make the voice sound deeper. (See How to have a deep voice?)

Studies have found that a person's voice pitch changes according to the people they are talking to. It was found that a man's voice might sound deeper when he speaks to a woman he finds attractive and less deep when speaking with intimate friends.

Studies have shown that too much alcohol consumption can lower testosterone levels. This could in turn lead to a high pitched voice. (See How does it feel like to have high levels of testosterone?)

Even after puberty ends a man's voice still become a little deeper later on. By the end of twenties the voice stabilizes then it can deepen again after the age of 45.