Puberty isn’t yet completed
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 testosterone levels
Low levels of testosterone can prevent a man from developing a deep voice.
You feel anxious around people
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.
You speak fast
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?)
You are speaking with close friends
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.
Too much alcohol
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?)
You are still young
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.