Type 2 diabetes tends to occur in older people and is associated with excessive weight. Type 1 diabetes although it can occur at any age usually tends to occur in younger people in whom weight is usually normal. Type 1 diabetes usually presents with people feeling unwell (thirsty, passing more water than usual, weight loss).
There may not be any symptoms beginning with Type 2 diabetes. As a result Type 2 diabetes can go undetected for a number of years before it is diagnosed and on average it has been present for 6 years before it is diagnosed. Diagnosis is on the basis of blood tests.