Thanks for writing in,
Knee pain in this age group is usually due to age-related wear and tear of joints. Pain is usually more while walking or squatting or sitting cross legged. Treatment varies according to the severity of wear and tear.
Ask him to avoid stairs, sitting in floor. Use only western type lavatory. Use pain killers cautiously. Hot packs, gels can also help him.
If pain is more, then consult an orthopaedician and follow his advice accordingly.
Hope this helps.
Wish him a speedy recovery.