Hi Zaidi thanks for your question.
Your 62 year old diabetic and hypertensive that is having blood pressure and is taking medicine for both Diseases, additionally your taking SHELCAL 500mg ,Shelcal is calcium,which doesn't have much side effect ,however some side effect ,which are bothersome but not dangerous are:
,gas and constipation
Some serious side effects are:
Change in hear rate
Signs of allergic reaction
like itching and rash
Yes, you can take small doses of calcium for long time.
Yes calcium can get deposited in kidneys and cause stone formation,but that is with higher doses for very long time.
No calcium doesn't cause gall bladder stone
Hope i answered your question