From the Guidelines

Diabetes Mellitus (DM) screening should commence at age 35 years.

According to the most recent guidelines from the Diabetes Care journal 1, screening for prediabetes and type 2 diabetes should begin at age 35 years in adults without risk factors.
However, for adults with overweight or obesity and one or more risk factors, screening should be considered at any age 1.
The American Diabetes Association recommends screening for diabetes with the FPG test beginning at age 45 years and at a younger age for individuals with risk factors such as family history, overweight, and hypertension 1.
Other studies suggest that screening should be considered in individuals 45 years of age, particularly in those with BMI 25 kg/m2, and in people who are 45 years of age and who are overweight if they have another risk factor for diabetes 1.

The screening test can be either FPG, 2-h PG during 75-g OGTT, or A1C 1.
If results are normal, testing should be repeated at a minimum of 3-year intervals, with consideration of more frequent testing depending on initial results and risk status 1.
Risk-based screening for prediabetes or type 2 diabetes should be considered after the onset of puberty or after 10 years of age, whichever occurs earlier, in children and adolescents with overweight or obesity and who have one or more risk factors for diabetes 1.
It is essential to consider the patient's risk factors, such as family history, physical inactivity, and hypertension, when determining the screening age and frequency 1.

From the Research

The recommended age for commencing Diabetes Mellitus (DM) screening varies among different studies and guidelines.

The US Preventive Services Task Force (USPSTF) recommends screening for prediabetes and type 2 diabetes in adults aged 35 to 70 years who have overweight or obesity 2, 3.
The American Diabetes Association (ADA) recommends screening all patients older than 45 years for prediabetes and diabetes, and screening earlier for patients with risk factors 4, 5.
Another study suggests that screening guidelines should be stratified by body mass index (BMI), age, and prior test history, and that the recommended diabetes screening policy should be stratified by age and by finer BMI thresholds than in the status quo 6.

Screening eligibility is often based on age, body mass index (BMI), and other risk factors.

The USPSTF suggests considering earlier screening in racial and ethnic groups with high diabetes risk at younger ages or lower BMI 3.
The ADA recommends screening earlier for patients with major risk factors, such as family history, physical inactivity, and certain ethnicities 4, 5.
A study found that screening all adults aged 35-70 years regardless of BMI yielded the most equitable performance across all racial and ethnic groups 3.

The frequency of screening also varies among different guidelines and studies.

The USPSTF recommends repeating testing every three years if results are normal 2, 5.
The ADA recommends screening for type 2 diabetes annually in patients 45 years and older, or in patients younger than 45 years with major risk factors 4, 5.
A study found that an optimal screening policy would generate higher net monetary benefits and save health expenditures per individual in the US above age 45 6.