How do doctors know if you have type I or type II diabetes?

They see you have high blood sugar so they know it is diabetes. Do they just go by age and assume it is type II or is there more to it? I know 2 people who were diagnosed with type I diabetes late in life (24 yrs old and 27 yrs old). What is the determining factor?

Okay. No one has actually answered my question. I know the difference between type I & Type II. Type I - pancreas not making insulin, Type II insulin resistance. I know Type I can be diagnosed later in life and they are now starting to diagnose type II in kids. The question is How do doctors figure out which one you have? What tests are done to see if you aren't making insulin properly or if it is a resistance?

type 1 is where u are born with it
type 2 is where u get it wen u are an adult/young adult

The diagnosis of type 1 diabetes, and many cases of type 2, is usually prompted by recent-onset symptoms of excessive urination (polyuria) and excessive thirst (polydipsia), often accompanied by weight loss. These symptoms typically worsen over days to weeks; about a quarter of people with new type 1 diabetes have developed some degree of diabetic ketoacidosis by the time the diabetes is recognized. The diagnosis of other types of diabetes is usually made in other ways. These include ordinary health screening; detection of hyperglycemia during other medical investigations; and secondary symptoms such as vision changes or unexplainable fatigue. Diabetes is often detected when a person suffers a problem that is frequently caused by diabetes, such as a heart attack, stroke, neuropathy, poor wound healing or a foot ulcer, certain eye problems, certain fungal infections, or delivering a baby with macrosomia or hypoglycemia.
Diabetes mellitus is characterized by recurrent or persistent hyperglycemia, and is diagnosed by demonstrating any one of the following:[3]
fasting plasma glucose level at or above 126 mg/dL (7.0 mmol/l).
plasma glucose at or above 200 mg/dL (11.1 mmol/l) two hours after a 75 g oral glucose load as in a glucose tolerance test.
random plasma glucose at or above 200 mg/dL (11.1 mmol/l).
A positive result, in the absence of clinical symptoms of diabetes, should be confirmed by another of the above-listed methods on a different day. Most physicians prefer to measure a fasting glucose level because of the ease of measurement and the considerable time commitment of formal glucose tolerance testing, which takes two hours to complete. According to the current definition, two fasting glucose measurements above 126 mg/dL (7.0 mmol/l) is considered diagnostic for diabetes mellitus.
Patients with fasting glucose levels between 100 and 125 mg/dL (6.1 and 7.0 mmol/l) are considered to have impaired fasting glycemia. Patients with plasma glucose at or above 140 mg/dL or 7.8 mmol/l two hours after a 75 g oral glucose load are considered to have impaired glucose tolerance. Of these two pre-diabetic states, the latter in particular is a major risk factor for progression to full-blown diabetes mellitus as well as cardiovascular disease.
While not used for diagnosis, an elevated level of glucose irreversibly bound to hemoglobin (termed glycosylated hemoglobin or HbA1c) of 6.0% or higher (the 2003 revised U.S. standard) is considered abnormal by most labs; HbA1c is primarily used as a treatment-tracking test reflecting average blood glucose levels over the preceding 90 days (approximately). However, some physicians may order this test at the time of diagnosis to track changes over time. The current recommended goal for HbA1c in patients with diabetes is <7.0%, which is considered good glycemic control, although some guidelines are stricter (<6.5%). People with diabetes who have HbA1c levels within this range have a significantly lower incidence of complications from diabetes, including retinopathy and diabetic nephropathy.[14][15]

a bloodtest and the symptoms you describe.

Type 1 diabetes is characterized by resulting in the body's failure to produce insulin, the hormone needed to convert sugar, starches, and other food into energy needed for daily life.
Type 2 diabetes results from the insulin resistance (a condition in which the body fails to properly use insulin) combuned with relative insulin deficiency.
Type 3 diabetes occurs develops when a woman is pregnant, and it goes away when the baby is delivered.

Diabetes type 1 usually starts early in life. Type 2 later in life. It's found when doctor does lab tests. Thirst and loss of weight are two prominent symptoms. Type 1 people must use insulin shots and type 2 uses medication(pills). High blood sugar (glucose) is found mostly. Anything over 200 is considered high.

No type 1 diabetics are not defined by "they are born with it." I'm a type one and I was not born with diabetes.

Basically type one is found in younger kids/teens/adults. And it's where their pancreases no longer work at all or barely work, therefore requiring type one's to take a immediately effective shot.

Type 2 is most commonly found in older adults, from being overweight, genes, or there pancreas isn't making enough insulin to keep the sugar under control. HOWEVER, theirs still works pretty well to an extent that is why most take pills, and it disperses over time.