Does a calcium score of 0 rule out chest pain being cardiac related? or is a ct angiogram possibly still warranted ?

Some other coronary artery conditions can rarely cause chest pain with low or zero calcium score and CT angiogram may not be helpful except in case of coronary artery dissection. I can say the probability of atherosclerotic coronary vascular disease as the cause of chest pain is very low or almost nil with a calcium score of zero but other causes of angina pectoris can't be ruled out entirely.

No, a calcium score will not rule heart related conditions that can cause chest pain, will make one mechanism/ ischemia less likely. There are inflammatory heart conditions more likely at your age, such as pericarditis or myocarditis among many others for which a calcium score will be useless in diagnosis.