I think this phenomenon can be split into two sub-categories. There are the books which are for all intents and purposes absolutely children's books that provide a sense of nostalgia and escapism for adults (which Harry Potter provides to an extent with its old-fashioned school setting), while the other type are the books which simply break down all feeble attempts at pigeon-holing to an audience and age range. Wolf Brother by Michelle Paver is one of the latter.
Now, before I give the synopsis of this story, I will say that I'm about to mention some things that sound like spoilers, but in actual fact this happens right within the opening paragraphs. Still, you have been warned!
Wolf Brother is set in the Stone Age some 6000 years ago, and tells the story of a young boy called Torak. He and his father were attacked by a bear (or is it?), which kills his father. Alone and terrified, Torak must fend for himself in the wild. But he soon befriends a wolf cub. Together they travel the land, learning about a growing and mysterious evil while being stalked by it.
Wolf Brother might just be one of the most well-realized worlds of fiction I've ever read. It's clear from the get go that Paver researched this first hand, not just from secondhand sources, by the way she pulls on all of the senses in her writing. Evocations of smell, sounds, touch and taste occupy the world just as much as sights, bringing a sense of immersive sharpness to it all. Paver is also a very tight, taut author: no word is wasted or superfluous. Everything either advances plot, builds character or deepens the atmosphere. It makes for an intense, almost visceral read. It doesn't hurt that the story itself is absolutely cracking as well!
But most impressive of all is the ingenious balancing act that Paver pulls off. This is clearly the Stone Age, right? But is it true-to-life Stone Age? Well, at first glance you'd say no: there's talk of magic and the supernaturial, after all. But is it real magic, or just superstition? Paver plays a balancing act by never really committing to either: it's down to the reader to interpret. Is that red moon really red? Or is it a lunar eclipse? It's up to you!
And that's one of the finest hallmarks of a book that extends across the ages: this elbow room for the reader to decide what they think is happening and what it means. This multilayered writing is extremely tricky to pull off, but when it works it results in that magical kind of story that you can read as a child and as an adult and feel as though you have experienced two different stories. It is the sign of a highly skilled author, which Paver definitely is.
Wolf Brother is an all around wonderful read, and the reasons to go and grab it right now are multiple. There are basically no reasons to avoid it...including how old you are.