Section 39. Except as hereinafter provided no contestant who is under eighteen or who has reached his thirty-fifth birthday shall be permitted to engage in any boxing or sparring match or exhibition, except that said age requirement shall not apply to a boxing champion of the world who is still active as a professional boxer, or to a former boxing champion of the world who has not been inactive as a professional boxer for a period of more than two years from the date of his last boxing contest, and except that an amateur boxer shall be allowed to compete as such at the age of sixteen. At the discretion of the commission a professional boxer who has reached his thirty-fifth birthday may be permitted to engage in a boxing match if he passes a physical examination by a physician selected by the commissioners. At the discretion of the commission an amateur boxer who has reached his sixteenth birthday but has not yet reached his eighteenth birthday may be licensed as a professional boxer. The foregoing shall not apply to courses of instruction in boxing, boxing or sparring matches or exhibitions, sponsored and conducted by recognized boys’ clubs, youth organizations, schools or colleges, municipal or state park or recreational departments, or by incorporated private nonprofit boxing teams, under the supervision of qualified instructors and directors; provided, however, that any of the contestants thirty-five years of age or older shall be restricted and limited to sparring matches or exhibitions of three-two minute rounds and for fund raising for charitable organizations. No person under sixteen shall be admitted to or be present at any professional boxing or sparring match or exhibition unless accompanied by an adult.