I am 25 years old. Is it possible to have a heart attack?

Yes, but very low. In your age it is extremely unlikely. Only if you would have certain forms of abnormal lipids in the blood due to genetic mutation, anatomic abnormalities, severe prinzmetal's angina.
Extremely unlikely. The chance of a heart attack in a 25 y/o is very small. Cocaine abuse can potentially cause a heart attack. Also radiation treatment for cancer where the heart is within the treatment area can cause damage to the coronary arteries. There are other problems with the heart or other chest structures, so you should probably get it checked out v.