Do consult an Speech Therapist and if needed a Phonosurgeon.

During puberty in males the mass and length of the vocal fold increase and the pitch decrease. Few of the people although having the appropriate vocal fold mass and length after the puberty, but they are not able to switch to the new low pitch voice (male like).Mostly  its reason can be usually long time habits from childhood, speaking into a high pitch voice. In this case only thin edges of vocal cords vibrates and also the whole length of the vocal cord does not vibrate. Consult voice therapist for further advice...