Could a 16 year old have a heart attack?

It depends: Current guidelines recommend that all kids be screened for high blood lipids at least once when they're between 9 and 11 years old and again between 17 and 21. See: http://kidshealth.Org/parent/medical/heart/cholesterol.Html# especially see those that should be checked if there are certain risk factors.

Yes.: Use of certain drugs can cause a heat attack.

Extremely rare: It's extremely rare. The causes are: anomalous origin of a coronary artery, vasculitis, coronary spasm, coronary embolism and early onset type I diabetes. That said, the most common cause is cocaine use.