Ex 13 :

  if ( age >= 13 and age <= 19 ) printf("Teen Age");
  if ( age >= 20 and age <= 35 ) printf("Young Age");
  if ( age >= 36 and age < 50 ) printf("Middle Age");

should read as :

      if ( age >= 13 && age <= 19 ) printf("Teen Age");
      if ( age >= 20 && age <= 35 ) printf("Young Age");
      if ( age >= 36 && age < 50 ) printf("Middle Age");