AMAZING. Deserves the fifth star.
This book should be worldwide required reading. It's YA at its best.
As for what age you should be to read it, I think twelve is pretty good. I read it about a week after I turned eleven, but I'm pretty mature when it comes to books. It's a good introduction to young adult literature. It doesn't really go farther than kissing and some light discussion, which shook me a little at such a young age, but as far as YA goes, it's rather appropriate. There's plenty of swearing, but the only time some thing truly offensive (a homophobic slur) shows up, it is put in the light it deserves: it's shown as truly offensive.
This book is wonderful in ways far too difficult to put into words. Yes, in today's world, it's far from revolutionary and slightly dramatized. But it was written in, and takes place in, Georgia in 2014. And the message transcends generations. I personally believe that this book almost singlehandedly made my best friend feel okay about coming out.
The romance in this currently tied for my favorite literature couple of all time. It may not be 100% realistic, but that's the magic of books. It's so well written, and worth rereading a thousand times (which I might have actually done; I think I could recite this book). It's perfectly sweet and beautifully genuine.
This was the book that made me want to read YA. This was the book that made me see the world in a different light. This book changed my life.