The commonest reason for knee pain in this age is osteoarthritis, i.e. degenerative changes in the joint surface causing rubbing of bony surfaces against each other causing pain.
Next Steps
You should start with hot fomentation, take analgesic medicine,
calcium and vit d supplement, apply analgesic ointment. You should get X ray of Knee joint to know the details of the condition.
Health Tips
Avoid sitting down, avoid heavy work, avoid Indian toilet, avoid stair climbing and descending.