I don't think I prefer writing for one age group above another. I am just as pleased with a story which I feel works well for very small children as I do with a story for young adults.
New Zealand is the only country I know well enough to write about. It can sometimes lead to complications.
I once knew a house rather like The Land of Smiles - an old house occupied by a varied collection of young people, mainly students. However none of these people were true models for the characters in the book, though their way of life may have been.
When you are writing, of course, you have to do all that writing and correcting for yourself. When I was a librarian it was expected that I would know about a wide range of books.
Every writer has to find their own way into writing. Margaret