Sounds like your son is at least pre-diabetes. If he isn’t diagnosed T1D, suggest pushing for antibody testing. My other thught is the GM might be a misdiagnosed adult onsetT1D, as an estimated 10% of T2Ds are acutually T1D.
If antibody positve, that should get your son ongoing attention and supplies to closely watch his condition and, possibly, treatment that will delay onset/slow progression of the disease.
The year after I was diagnosed as T2D, my daughter was diagnosed T1D and in ketoacidosis. After twenty six years progression and antibody testing, my diagnosis was changed to adult onset (LADA) T1D. And my GM was adult onset diabetes, that being before antibody testing. I think it likely she was actually adult onset T1D.