I would suggest that you have him checked for diabetes just the same to make sure.
Could be a growth spurt. If he is eating refined carbs/sugar that makes you hungry all the time. Protein and fat fill you up.
When he feels hungry an hour after having eaten a good size well balanced meal, tell him to have a drink of water or some other liquid. If he still feels hungry after 20 minutes then to have something to eat - like a piece of fruit, some ham, small portion of cheese, egg.
Make sure that he eats a well balanced and healthy diet with foods that have slow release energy. As you have diabetes, you will know what I am talking about.
Sometimes our brain cannot distinguish between hunger and thirst. This is what were all told when attending weight watching clubs. And that is the advice they gave was to have a drink and wait 20 minutes before having something healthy to eat.
It is possible that he may be going through a growth spurt. I don't really exactly at what age growing stops, but each child/teenager is different.
If he was feeling hungry and losing weight and felt ill then I would be worried.
Increased appetite could a sign of low blood sugar, diabetes, depression and anxiety. Diabetes can be ruled out since you have checked his sugar and there seems to be no problem with his blood sugar since he is active. Check his emotional state. If he is happy as before and does not experience mood swings and isnt under the influence of any intoxicants then any sort of depression can be ruled out. The only thing that i can advice right now, is a thyroid test. If his thyroid levels are okay, then you can relax. Its his growing body thats demanding more nutrition and he feels hungry all the time.