I was 20 when I was officially diagnosed as type 2 diabetic, however by that time I already had some complications.
On hindsight it truly seems that I was diabetic/pre-diabetic/carb sensitive or something like this, since I was 10 years old.
I have 2 brothers and 1 sister, we all at the same home cooked family meals, our mother would bake every Friday ahead for the weekend. I was the only chubby but not fat one in the family, all the others were and are slim. It was noted that I would become very drowsy after meal times, whereas the others wanted to go out and play, all I wanted to do was go to sleep.
Parents took me to Drs, tests were carried out but nothing conclusive came up, although my Dad remembers the old family doctor, who had retired way before, said to watch me as I am going to be diabetic. Sure enough then it happened, at the time of diagnosis nobody could believe I am type 2 on account of my age, even less so when it was discovered that going by the complications that had already set it this type 2 diabetes must have been brewing along there in the background for some time.
Now of course its not quite so rare to hear of children being diagnosed type 2.