Max is 13 as I write this and got the travel bug from traveling with me and his mom and stepmom overseas, in the US, and in Canada. When he asks the question about traveling alone, he’s really asking something more like “how old do I have to be before I can buy a plane ticket and go to Hawaii by myself?”
He can do it right now, so long as he has a ticket, a government issued ID, and gets on the right airline. When he turned twelve, he was considered a “young adult” and could fly wherever he wanted in the United States on American Airlines, United Airlines, and Southwest Airlines. For Delta, the largest US airline, he will need to be 15 to buy a ticket and jet off all by himself to, say, Toledo. Assuming he wants to go to Hawaii, however, Hawaiian Airlines will let him travel there alone at age 12. Same goes for US Airways, the fifth-largest airline in the US.
There are no laws or legal regulations that control how old a passenger must be in order to travel on an airplane alone. Instead, the US Department of Transportation has left it to the airlines, which have set the age at either 12 or 15 for kids to travel alone without any restrictions.