I'm sorry I haven't had time to post in this thread before. Since this taps my field, I'll give a scientific background and a scientific solution.
Studies of children and teenagers have shown that teenagers indeed do have a tendency to fall asleep later at night and wake up later in the morning. This is due to the chemical process (I won't go into details, I can if someone is interested) that starts in the body at the end of the day when our biological system starts to prepare us for sleep. This chemical process has a slower onset in teenagers, which means that they actually do get tired later at night than preadolescent children do. The optimal time for teenagers to sleep according to the biochemical rythm of them have, is between midnight and 9 am. No differences between boys and girls have been found.
The bad news is that this biochemical sleep process is slowest after onset of puberty, which means that if your son is 13, it will probably only get worse from here on. The good news is that habits influence this biological process more than genetic determination, so it's not that difficult to alter. This is what your son should do:
in the morning right after the time he should go up. Let's say he should go up at 7 am. Then have him go up at 7, and make sure he gets out as soon as possible. It's summer now, have breakfast outside, in the garden or at some nice cafe, take a walk, sit outside and read - anything that gives him daylight exposure for some time, at least 30 minutes, preferrable longer.
Turn off the light
in the evening. From around 8-9 pm he should stay in dark rooms, and like others have pointed out, not occupy himself with arousal increasing activities. No physical exersise or exciting computer games at this time of the day, reading or passively watching a movie or something is better. By staying in darkness, the melatonin productions increases and with that, the tendency to get sleepy.
If this fails, I see no other solution than moving to Sweden
Based on the scientific studies I mentioned above, and Swedish studies showing that 9/10 teenagers have a late diurnal rythm and 50% of all teenagers are sleep deprived, several Swedish high schools and collages have started experiments with evening classes. When he gets older, he can become a scientist. We are social misfits for ever - we work when we are alert and awake, be it from 5 am - 3-4 pm like my professor here, or from 11 am - 6-7 pm and then again between midnight and 2 am, like myself and many of my friends