After puberty which is around the age of 13-14, under the influence of testosterone in the body, beard gradually started developing . For the growth to become thick it takes a few years maybe by the end of a adolescence . The density and the pattern of beard has a genetic component and it would vary from person to person. If you do not develop a proper beard by the age of 20 then you might need further evaluation. Also examination needs to be done to check for the presence of chest hair axillary hair and pubic hair. Some tests are advisable and a proper history evaluation to make sure it is not a hormonal problem. If the cause is not hormonal then hair transplant can be done for your problem. I have done several cases of hair transplant for beard and moustache and patients are very happy with the new look. You should send me images through private online consult for a better assessment of the problem and approaching it accordingly. Hope this is helpful.