If i had a normal a1c of 5.4 in july 2016, and you didn't take care of yourself can 6 months later can it develop to diabetes now.

No, but: you need to take care of yourself if you have any of the several risk factors for developing type two diabetes as overweight, smoking , high uncontrolled blood pressure, smoking, inactivity, etc... Regular checks and leading a healthy lifestyle are the key for early discovery/prevention, best wishes

Diabetes.: There's a genetic predisposition to diabetes which can be more easily uncovered if one doesn't care for oneself as far as diet, exercise and weight management. But type 2 diabetes does take time to manifest, so six months may not be enough time to go from normal to full-on diabetes. That being said, diet, exercise and weight management are always important, diabetes or not.