One thing many are wondering is why many people who are now adults, in school. People like Harry, Ron, Hermione and Draco, why are they going to Hogwarts? The answer is simple. Though they are not kids, their education was left uncompleted. After all these years, the students have been called back to complete their education at Hogwarts. Some people did go to Hogwarts the year that Voldemort took over, but that was hardly a proper education. Hence, these people have not reversed in age, but are completing their studies.