Until recently, diabetes was classified by age. What is now called type 1 diabetes was known as juvenile-onset diabetes and type 2 diabetes was known as adult-onset diabetes. However, type 1 diabetes can occur in adults (though usually young adults), and type 2 diabetes is increasingly being seen in children because of the rise in obesity.

Type 1 diabetes involves an inability to produce insulin, which is required to break down glucose (blood sugar) for the body to use as energy. It is usually diagnosed before age 40. About half of all people diagnosed with type 1 diabetes are younger than 20 years of age, according to the American Diabetes Association. Younger people are also at risk for maturity-onset diabetes of the young (MODY), a genetically acquired form of diabetes.

Type 2 diabetes, by far the most common form of diabetes, occurs when the body produces insulin but is unable to use it properly to break down glucose. It is most often seen in older adults, with half of all cases diagnosed in people 55 and over, according to the ADA.

Age plays a significant role in the risk of developing type 2 diabetes, especially after age 45. Because aging is an inevitable process, prevention strategies focus on diabetes risk factors that can be controlled, such as diet and physical activity.