Welcome to e health forum.
Yes, it is common in some young individuals to feel their cardiac pulsations in the epigastric region or upper abdomen.
Since most of the tests including the CT scan, have shown to be normal, there is absolutely nothing to be worried about.
Some risk factors that can predispose to have aneurysms include - caucacian race, Male sex, age above 60 years, high blood pressure, smoking, and family history. In your case, you do not have any such issues and hence are not at risk of having aneurysms currently.
Relax for the time being and improve your fitness by joining a gym and this will help you control your palpitations. In addition, you may consult your doctor to rule out conditions like hyperthyroidism, hypertension, cardiac rhythm disorders, which may be the cause of your palpitations.
I hope this helps.