Is diabetes more common in certain age groups, ethnic groups, or gender?

Yes. More common in hispanics, african americans, american indians happens at lower weights in oriental , asian indian populations more common in older folks, but nopw occuring in even kids/teens -overweight = between sexes.
Yes. Type ii diabetes or Insulin resistance is more common as you age. Usually begins around age 40 but now due to poor eating habits is beginning as young as early teens. It is associated with obesity but not exclusively. African americans are at higher risk, primarily because the darker skin leads to lower vitamin d levels, low vitamin d is a risk factor for both type i and type ii diabetes.