Most common cause of knee pain in this age is osteoarthritis. I would suggest u kindly to get a knee x ray done and consult an orthopaedics sugreon. If the arthritis is of a lower grade conservative approaches like hydrotherapy , viscosupplementation , short term pain management , footwear adjustment may provide relief (depending upon the x ray) . In high grade osteoarthritis with deformity , Knee replacement remains the only plausible choice.