Theres no difference, same thing.
While the causes of this may be present or start while young, they normally only develope to a problem when a person is older. Most are over 60yrs old, but there is a small percent in their 30's and 40's.
Having an EKG, checking a person blood presure and cholesterol level may help identify signs of it, but the only way to really see if a person has it, is by having an angiogram done where they take an X-ray to see the blood flow in the arteries after they inject a sorta dye in the them.
School children ages 11-15, really wouldn't be effected with CAD, but they can have a heart problem called Kawasaki Syndrome with can cause a simular heart problem.