I commend you for wanting to give a Bible to your nephew; is there anything you could give him that would be more valuable? God gave the Bible to us, and through it we discover His love for us. We also discover how He wants us to live. The psalmist wrote, "How can a young man keep his way pure? By living according to your word" (Psalm 119:9).
This is why I hope you won't be discouraged over all the different Bibles that are on the market. (I say "different Bibles"—but of course, they are all the same Bible. They only differ from each other in appearance or binding, or in the translation that is used, or the explanatory notes that are sometimes added.) Your local Christian bookstore or other knowledgeable bookseller can help you, and you shouldn't hesitate to ask for their assistance.
What should you look for? First, I suggest you get a generally accepted modern translation that is easy to understand. Then consider what is called a "study Bible"—that is, a Bible that also includes helpful notes and articles explaining each book or passage. Some are designed specifically for young people.
Most of all, encourage your nephew not only to keep his Bible, but to make it part of his daily life. The Bible says, "Do not merely listen to the word. ... Do what it says" (James 1:22).