I would say the book is appropriate for ages 6 to 12. There aren't any really big words, but it's not a super-low reading level either.
There's not really anything scary or rude about this book. There's a spider who threatens to eat the hummingbird, and a squirrel who could use some manners, but other than that, it's pretty tame.
There may be some boys who would be interested in this book, but since it's about fairies, and more specifically a girl fairy, girls may be more attracted to the story.
I would recommend this book to young readers who are interested in fairies that aren't particularly glittery.