The wall is wider and just one big wall not like it have another layer because of your rank
If you are in the middle you can't see the walls but if you get closer and closer your going to realize that it's a big wall
The people in the middle have the good materials where they can build a huge building and technologies
While the people that close into the wall have a poor materials that they can only make the house like wooden or stone, they also have don't technologies that in the middle have
The people in the middle have this power that they called "quirks" where 90% of the population have it and the 10% are quirkless, most of the quirkless ended up killing them selves because of they difference to other people
While the people close into the wall don't have this called quirks. And since they are near the walls some years the giant human eater called titans are attacking, since they don't have quirks they create an technology to kill titans. And the only can used this are the SOS -you know the squad don't make me fool-
The people in the middle don't know about titans or what happening on the other places they are so busy of being an hero and villains. They are training an middle school students to be a hero and save the people that in danger.
While people close into the wall training an volunteers to kill titans.
The government only knows what between the both place some of the squad can go to the mid and go back just like having an vocation some times it's an order or a mission. And the people even heroes can't go to the closer the walls.
You must thinking why the people that have quirks just go closer the walls and and helped to kill titans since they have superpowers?
Well a person with an quirk are cocky and they don't want to help the quirkless since they are worthless they think that they just going to die if they worked with the quirkless so the government just remove all the information about the closer wall and titans.
In this AU there is also an another foundation, where all the abandoned kids or babies will take and trained them to be an titan killer. So don't confused of "how did an child can used the odm gear?"
Izuku is 2 years younger than Levi. Like the canon Hange is 2 years younger than Levi, and Erwin is 4 years older!!