The normal age for going to college is 18 or 19. People can go to college at the age of 15 because they study well. Primary and secondary schools have advanced placement, unlike our normal students who have to go every grade. Children who can be divided into classes in advance are smart and logical, and it is a waste of time not to divide classes in advance! Their intelligence can get in touch with some advanced knowledge and fields in advance, and they don't need to waste time at the lower stage.