Post some of his music so we can hear
The best thing you can do is encourge him to keep practicing. That's the only way anyone can get better, regardless of how talented someone is. Of course, a good way to speed up the learning process is to listen to lots of music in his particular interest, and to study the sheet music. Also, it may help if he had his own niche. For example, some of the composers in this forum are exclusives, such as myself. I focus on one type of composition style, romantic piano writing, and I am very good at that particular type of style. I could go into other styles, but they wouldn't be very good, and my true niche, which I have acquired and developed by hard work, is in romantic piano writing. Had I gone all over the place, I probably would be mediocre in all styles, which wouldn't be impressive.
If someone goes all over the place with many different styles, it is hard to capture the interest of critics, and in my opinion, finding a niche and sticking to that niche is the best bet for any composer on this site, not just your son.
Now if you are asking about actual lessons or music theory, there are many tutorials on the web, or you can order music theory books from amazon, or even go to a place like Barnes and Noble to find a good music theory book. If you are asking, "should he go to a music college", well, this is up to him. If he wants to choose music as his career, then I don't see why not. He would be surrounded by lots of musicians, and
may even have an easier time getting his works exposed to the public. But if he wants to get better at composition, going to a music school will not necessarily help someone become a better composer. Just as, going to college does not necessarily mean success. In fact, I think college is very limiting, not just in music, but in ANY field. College doesn't show the way to being successful
on your own, all college really does is prepare the average student to work for someone else. The point? You can't rely on someone else, or school to help that person achieve success. It is completely up to the individual, and how the individual utilizes the available information, whether it be school, books or the internet.