I hope I'm not being too blunt but tbh it just sounds like you're just overthinking things. Personally, I just see being a "Little" as another label that we identify with to better understand ourselves. Are you gonna fit perfectly in that box? Of course not, but it'd also be way more boring if you did! Maybe you have hundreds of stuffies, maybe you don't have any. Maybe you love Paw Patrol, or maybe you're more into Avatar/Anime. You could be anywhere in between or something else entirely, but no matter who you are, you're not alone. Your little age (as I've come to understand it) can range anywhere from literal newborn to teenager so don't sweat it if yours isn't what's perceived as common. Don't worry so much what others think is "normal" (by Little standards or otherwise) just do what you like, and as long as you're not harming yourself or others then what does it matter what it is? If coloring makes you happy, then get a coloring book and go at it. If cartoons are your jam, then watch them! Whatever it is, as long as it sparks joy, go for it. If you keep comparing yourself to what you "should" be then you're only ever gonna find faults and imperfections. So try not to worry so much about not being "little enough"
Side note: I don't think the things you listed off are as big of a deal as they sound in your head; I'm ace and neurodivergent too so I can personally assure you you're not the only one
Also the reason it probably seems like all the Littles and CGs are from the US is probably bc the US has the 3rd largest population in the world (it's essentially like 50 seperate counties combined anyway, someone from California and someone from New York wouldn't exactly be able to popover at each others houses on the weekend for playdates lol) but anyway, my point, I guarantee there are others like you where you are too, sometimes you just gotta search em out
Once again, I hope I didn't come off as rude or drone on too long, just trying to be helpful, you're not alone in this