To examine the differences in physical activity (PA) between older adults with and without diabetes/prediabetes and the correlates of PA frequency and associations between medical advice on PA and/or diet/weight loss and increasing PA among those with diabetes/prediabetes. Multinomial and binary logistic regression models using 2016–2017 National Health Interview Survey data (N = 4,860 aged 65+ years with diabetes/prediabetes). About 44.2% of those with diabetes/prediabetes, compared with 48.1% of a matched sample without, engaged in any PA three plus times a week. The low PA group (PA frequency was zero to two times a week) was more socioeconomically disadvantaged and had more chronic illnesses than the medium (three to four times a week) or high (five plus times a week) PA groups. Any PA and/or diet/weight loss medical advice was associated with two to three times higher odds of increasing PA. Health care providers should consider prescribing PA and/or diet/weight loss for patients with diabetes/prediabetes.