Does a normal ct calcium score scan eliminate possibility of atherosclerosis plaque build up in arteries?

Not entirely: Usually, a calcium score >100 indicates that calcium deposits are present & that coronary heart disease/obstruction is likely present. Scores between 0 & 100 are considered normal, but this may just indicate a very small amount of calcium that hasn't progressed to disease yet. At your age, follow heart disease prevention--non-smoking, healthy eating/exercise, not calcium score. Good wishes:)