Many factors. Many factors contribute to the complications of diabetes. The duration of the disease is definitely an important and in my experience it takes usually 10 years for significant complications. The rate of complications is also very much determined by the level of control. Very good control of blood sugar, blood pressure, lipids, and a good diet can delay diabetic complications by many years.
Time may vary. Time may vary depending on the individual.
Labs and routine che. Labs and routine check ups will detect complications. Specifically look for kidney disease, eye problems, neuropathies, heart problems etc.
See below. 1. No warning until too late in most cases--that's why all patients with diabetes are told to see eye md once yearly to catch something that can still be treated gets blindness. Nerve trouble often does present early to patient with pins/needles, tingling sensations at night, starting out in feet kidney damage gives no warning of progression -check yearly urine for protein leak.
Ge evaluated. Do not wait for symptoms to appear. If you have any family history, get yourself tested and possibly prevent complications.