Target age-groups for fiction

There are various types of books that are each generally targeted at a specific age group. Let's enumerate them here:

• Adult (18+)
• New adult (18 to 30)
• Young adult (12 or 13 to 18)
• Juvenile (0 to 11 or 12)
• Tween (9 to 12)
• Intermediate (8 to 12)
• Middle grade (8 to 12)
• Junior (7 to 8)
• Easy readers (about 4 to 7; for children just starting to read by themselves)
• Picture books

Most of these categories are just publishing constructs/standards, which means publishers use them to target and market their books, in order to make money. Each may have specific requirements or conventions that aren't obvious.