Hello,
Thanks for posting your query.
Having coffee is not likely to cause any knee pain. Rather caffeine enhances the analgesic effect of various pain killers when combined together.
At your age the most likely cause of knee pain while bending your knees is osteoarthritis. These are basically age related degenerative changes in the weight bearing joints like knee and is characterized by joint pain and stiffness.
The treatment options include pain killers, hot fomentation, lubricating agents like glucosamine sulfate, chondroitin , dycerin, etc and some life style modifications and physiotherapy.
You can start with walking and aerobic fitness exercises, quadriceps strengthening, patellar tapping, lateral heel wedges, etc- under the guidance of your physiotherapist. Loosing some extra pounds might help in early improvement.
No to Stair case, squatting postures, any chair which has a sitting platform lower than your knees.
Knee brace can also be used for an earlier and prolonged relief.
In severe cases intra articular injections of steroids and hyaluronic acid may be needed after consultation with your orthopaedician.
I also encourage you to consult an orthopedician for physical examination. A few blood tests, X-rays of the knee, CT / MRI scans of the knee will help us diagnose the condition and help us in choosing the best approach of treatment.

I hope this answers your query effectively.
In case you have additional questions or doubts, you can forward them to me, and I shall be glad to help you out.
In case you find my answers satisfactory, please do click on accept button.
Wishing you good health.
Regards.

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Hello.

Thanks for writing again.

For calcium supplements you can ask your orthopaedician to prescribe you coral calcium or milk calcium instead of shellfish calcium.

Hope my answer is helpful.

Wish you good health.

Regards.

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