Cartilage destruction in old age can be due to wear and tear of prolonged use. There are different grades of cartilage destruction. Early stages can be helped only by medicines and exercises but as u mentioned that you cannot walk more than 5 minutes without pain , so I think you are falling into late stages in which only total knee replacement is the only choice. It will help u in pain free movements of knee and you will be able to walk comfortably without pain. If you stuck up into non surgical methods than u may acquire
Diabetes, Hypertension due to non movability.
Next Steps
post your x rays
Health Tips
you may have DM, HTN as u have not mentioned before. but remember Total Knee replacements are done to make a person movable and it is mostly done at your specified ages only.