I think Sean (my 15 yr old) grew and grew, ate and ate, and didn't put on weight or even lost some for a time. He doesn't have diabetes to deal with but I suppose it was normal that his body just couldn't keep up with his growth. He's 6ft tall now and has size 14 feet.
Poor Khaleb went from 15 kg to 13kg in about a month (January) and he is sitting at 14kg now. This was from the thyroid meds. His metabolism probably wasn't working very well before the meds. I was glad when things settled down. I am still making the choice to give extra insulin and food rather than limit his meals.
Glad that Ryan can do quite a lot himself. Is he okay with it all? Khaleb doesn't know any other life and is happy to hand his finger over and even though he has a little whinge when he sees the needles, he doesn't complain when he gets them. The anticipation seems worse.
Khaleb seems over the worst of his cold. We are coming into Winter so I expect he'll have plenty more. We have changed over to porridge for breakfast and I find it is better than weetbix (your wheetabix). I've had to buy some kitchen scales though as working out a portion size has been a bit hit and miss.
You might have to make an appointment with the dietician to work out bigger portions that are healthy and don't blow the carb budget. You probably shouldn't worry too much as I think in boys it is just par for the course that they get a bit gangly in the teen years. Soon enough, they start filling out and that is scary. My little boy is more a man these days.