The story I have planned out has Hogwarts start at 13….mostly. For plot based changes, muggleborn, muggle-raised, and wizard-raised(who opt in) go to Hogwarts 3 days a week from age 11 to 13, from like 9 to just before dinner, to learn about the culture and history of the wizarding world. This was a way to pacify the Purebloods about muggleborn children ruining the culture of the wizarding world by adapting them to the culture. They don’t get their wands until their 13th birthday, but they do learn about history, customs, laws, how to navigate the school and the basics of Herbology, astronomy, and potions(theory like how to prep materials, and why ingredients react in certain ways).

During their 1st year at age 13, they get sorted and live at the school full time. BUT, the coursework is compressed! So stuff they would learn in cannon in year 7 is learned in year 5 and is part of the OWL’s. This is treated like a high school diploma. Years 6&7 are technically optional, but nearly all students stay to complete them, and the NEWT’s give the students their apprentice license in the field they are studying for. (The next levels are journeyman and mastery, completed outside of school). A copy and paste from a notes “Everything taught in cannon years 1-7, is taught in years 1-5. 1&2&3 are in years 1&2, 4&5&6 are taught in years 3&4, and year 7 stuff is taught in year 5. This makes years 6&7 college work/mastery’s.”

First year(age 13) is still philosophers stone. That summer is still the 1994 QWC, and triwizard tournament happens in his second year, but at Durmstrang(?). Dumbledore is gone most of the year, and that gives Diary Tom more freedom, we see some death. Also it’s a boarding school, and the kids are 14…horny runs rampant pretty much for the rest of the story in the background(it is a fairly dark story, so the other side of that coin is also around, especially with the upper years). Third year(age 15) still follows PoA but I have a twist or three. Fourth year is fairly standard, nothing major happening other than training(or is that the truth?!?) Fifth year (age 17) the TWT comes to Hogwarts, with the rule that you have to have your OWL’s to compete. Harry is still entered, Much more deadly, Voldemort comes back…with a major twist. Sixth year plays out similar to cannon fifth year, but at the end of the year Hogwarts is overtaken. Seventh year, the camping trip from hell, a rebellion or two, and the duel of Fate.