Thoughts on Harry Potter

1. There is never any explanation of why the Mirror of Erised was originally for. Some possibilities:
   1. It's certainly a very dangerous thing, effectively duplicating a drug addiction without the various chemical side effects. So I guess it could be used in rehabilitation, if not that regarding addictions as diseases to be cured is a modern idea.
   2. It is also a very powerful spying.surveillance tool, although possibly only by accident. It shows details of objects and possibly their surroundings that the viewer didn't know. "I really want that prophecy... ah, it's in the Department of Mysteries on that shelf." This is especially significant because, in the Harry Potter universe, divination doesn't actually work, despite being widely studied.
   3. It would make an excellent tool for psychotherapy, giving much better access to someone's subconscious than Rorschach inkblots, Freudian slips, or similar (I assume modern psychology has better tests). The psychologist could ask the patient what he saw, or there might even be a lost spell or command that allowed you to see what someone else was seeing directly. Personally, I like this theory, possibly because I am not sure what I would see and and I would like to know. One problem with this theory is that the Mirror is older than psychology-as-a-science, but it is not hard to believe that some powerful wizard in the past was interested in the mind.
2. Hogwarts appears ignorant of the possibility of students who are married and.or have children (ideally in that order). On one hand, this isn't surprising, since the students graduate at about the same time they reach the age of majority (17), comparable to modern high schools. However, the Hogwarts was founded in the dark ages, when marriage by that age was common, especially for girls. Somewhere in the 12th century (i.e. about 200 years after founding) the Church made a law requiring girls and boys to have minimum ages of 12 and 14 respectively. Some possibilities:
   1. The wizarding community has long had a higher age of majority, and the muggle word is just catching up now. The problem with this is that it would make them stand out in a time when they were trying hard to be inconspicuous.
   2. Attending Hogwarts had a social role sort of like attending a university: it was something you did instead of (or before, or as a break from) having a normal life. The catch here is that they would get relatively few students, as a percentage. If so, wizards must have been a higher percentage of the population at the time. I would guess the change occurred during the Industrial Revolution, when improved sanitation cut the infant mortality rate for muggles and birth rates took a while to catch up.
   3. The Hogwarts processes have been heavily revised since founding. Children originally started and finished younger (and probably took different classes for different degrees). Starting at age 8, for example, would allow them to all graduate before their 15th birthdays, which would be young enough to fit in with new muggle adults. The problem here is that I don't remember any evidence for anything like this in the books. Instead, Hogwarts had a strong "timeless" feel.
3. Near the end of The Deathly Hallows, Harry goes to confront Voldemort while carrying the Resurrection Stone, and loses it in the subsequent encounter. (Fine, he deliberately left it and no one else picked it up.) At the time, Voldemort and friends were based in the acromantula (giant spider) lair in the Forbidden Forest. This actually serves as an excellent set-up for the future. I had always wonder how plot objects in stories wound up guarded by weird monsters.
4. The series makes heavy use of the "one solution" puzzle, where there is an obstacle that can only be overcome is one specific way. For example, you must drink the right potion to pass the black fire; a normal Flame-Freezing Charm just won't work. Similarly, somebody has to drink the green potion in the inferi cave, you can't just dump it out. Normally, this is my least-favorite bit of magic in fiction, since generally used by authors to excuse obvious plot holes. J.K. Rowling, however, gives us the Fidelius Charm (i.e. secret keeper spell) and the Unbreakable Vow, both of which are though-out forms of this. Instead of just keeping the story on track, they have though-out rules, which are are explored and exploited in the books.
5. My brother Billy once made a Harry Potter dueling game (computer game, single and multiplayer modes). I'm told it was better than the one on Pottermone, although I've also been told that the Pottermore one is terrible, so that may not mean so much. In any case, in the game you could use the Salvio hexia spell to extend the duration of protective spells like Protego. It turns out the "real" spell with this effect is the Fianto Duri charm.
   
   Note: The game has been changed and is still fun to play (although it allows certain exploits). It was back in development , but I don't know much much happened or its current status.

Response

I'm fairly certain wizards in the Middle Ages were more likely to keep to themselves in their own communities (these included Hogsmeade and Godric's Hollow for example), Part of the point of Hogwarts was keeping wizards together in one place hidden from Muggles. So Muggles finding marriage customs odd wouldn't have been as much of an issue. Wizards also live longer than Muggles, so having children later would probably be okay. Also it's my understanding that teenagers getting married was far more likely to be an upper classes thing, while lower classes would be more likely to be in their twenties (though I don't have date ranges/locations/citations for this). So going to school until 17 probably wouldn't have stood out much. I feel like 11 is a reasonable starting age, as it gives the wizarding children time to learn to read and write and other basic skills that are not taught at Hogwarts, though as you say, things could have changed over time and literacy might have been among the early lessons, especially in a time where literacy was not common. That's an really interesting idea to explore, thanks for bringing all this up!

1. Wizards also live longer than Muggles". Interesting. Is this just because of better medicine, or is it innate?
2. The typical age of (first) marriage in the Dark and Middle Ages seems to depend on the source referenced. Beyond that, it presumably depends on when and where. My understanding is that marriage age for peasants slowly increased over time, and the "twenties" number is for around 1500. I spent about 1/2 hour trying to find so real numbers when writing the original post, and I don't think I turned up anything before 1200 (although I could just be terrible at research). On the other hand, Wikipedia told me that the median age for menarche was 17 in Scandinavia in 1800, so there is clearly more going on here.

Wizards just live longer, I don't how well it's explained.

They probably live longer because they bounce if you drop them off a balcony. (That is to say, they instinctively use magic to keep themselves alive.)

I think they're also able to have children much later in life than Muggles typically are (the women, at least?), so there might some something inherent to it. But I also don't really understand if they age more slowly (like maybe the teenagers don't actually look 18 by Muggle standards when they're finished school?) or if it's the kind of thing where they age to adults normally then approach old age more slowly, or if they age normally then just stay old for a long time? Still doesn't explain how old some witches are when they have children?

1. If the age more slowly, it only kicks in after a while. Hogwarts first-years still look 11, after all.
   
   
2. If I understand fertility correctly, a girl is born with a large but finite number of ova (it might have been 10,000,000), which cannot be replaced (they are formed from embryonic stem cells). Her body is careless with them, and she has about 500,000 left when she reaches puberty. Thereafter, her body releases them at a rate of 1 per month (except when pregnant or breastfeeding), losing about 99.9% of them in the process. When the last of them is gone, menopause occurs. The ova also may degrade over time, since it is more difficult for older women to conceive children. Also, IVF works better with ova taken from younger women, paralleling the effectiveness of natural conception at the time the eggs were extracted.
   
   If all this is correct, I think menopause could easily be delayed, probably by reducing the 99.9% loss rate. That would be a separate change from extended lifespan, but I assume it would be evolutionary selected for, and the wizards are a distinct population (score one for blood purity). I don't think ova degradation could be easily fixed though, because whatever would work for them would also work for muggles, and we don't have it. My best guess would be that there is fertility magic that just never got mentioned because it wasn't relevant to teenagers. Or maybe their bodies are using it unconsciously. In fact, that could easily apply to all age-slowing.

We don’t know that they look 11 in the books 😉

Also seeing as they just naturally live longer than Muggles, delayed menopause might just go along with that. However, I would love to know more about the Healers (and both magical medicine and magical research in general) so I love the idea of fertility magic. Magical birth control is discussed in the fandom so it would go along with that too.

I assume that young wizards look like young muggles because some of them (e.g. Harry, Hermione) live with muggles without seeming (physiologically) out-of-place. And given how paranoid the Dursleys were about anything unusual about Harry, I think they would have mentioned if he grew slowly.

I think that effective magical birth control can be assumed because there are so few large wizarding families (name one other than the Weasleys). I think 8 children born and 3 reaching adulthood was common before the Industrial Revolution. I assume that most wizards reach adulthood, given the quality of magical medicine (also, we don't see many die at Hogwarts, and none of natural causes). Instead, wizard demographics match the modern West, which has cheap, unlimited birth control.

Harry was described as small and skinny for his age, and Hermione was almost 12 so who knows 😉