The world is never fair. It should show favor to the young, sparing them the emotional problems of illness and disease. Yet health comes come to everyone regardless of age, the status of the parents or the abilities of the children. In this, it's entirely possible for the young to lose their hair. In most cases, this is the result of the stress caused by serious illnesses and/or their treatments, e.g. chemo- and radio-therapy to deal with cancer. Less seriously, hair can be lost because of fungal infections, or the teens can literally be pulling out their own hair with the latest fashions including cornrows and comparable styles pulling the hair into tight braids and plats. Even male pattern baldness can begin as early as fourteen and fifteen. Fortunately it's rare but it's possible.
When it comes to treatment, it's easy to change hairstyle and to treat a fungal infection. But male pattern baldness is a different problem and, so far, finasteride is the primary treatment. When this drug was going through the clinical trials to gain FDA approval to extend the use from treating benign growths in the prostate, to preventing hair loss, the FDA was persuaded the evidence did not permit the drug to be given to the young. There's a limit. Doctors are not to prescribe this drug to anyone under the age of 18. Why impose this limit? Because there's very clear evidence that this can significantly affect the development of sexual identity. In older men, it can reduce libido, cause erectile dysfunction, produce testicular pain and increase the size of the male breast. These are not problems anyone would want to wish on the young before they have ensured the rite of passage into adulthood.
Although it's always possible a young man might persuade a doctor to ignore the FDA and write a prescription for off-label use, it's not worth the risk. Propecia, also sold as finasteride, should be used with care by older men. The potential damage to the younger person should never be ignored. People should wait before using Propecia.