There are a few gene (MODY) variants that contribute to development of type II. I have a fit 83 year old patient with a MODY variant. Her A1C was prediabetic 3 years ago. It now goes back and forth between diabetic-prediabetic range depending on her Vit-D levels and consistency of low glycemic diets.   Her fat son, on the other hand , went full ham insulin dependant diabetic in his 30's.