What is his purpose for owning one? Does he want to race, have something to ride out and about in nature or does he want to take up free style stunt riding. Sounds to me like he's given this a lot of thought and has had the discipline to save all these years. This show responsibility and commitment. The boy seems like he has a good head on his shoulders. I'd take the lead as a parent to make sure he enjoys this safely with some proper training, maybe Dad should get one also so they can both do this together.
I have to disagree with CozInCowtown, there are a lot of folks who enjoy these machines, young and old alike. As with anything that could be dangerous, early training and proper supervision will make this a safe activity for him. It's the uneducated boneheads that ruin it for most of us.