When your Shihan or Sensei asks people to work with someone their own age and then smiles in your direction you have a number of choices 1) sit and watch, 2) pick any injury that is believable ... which can be anything if you're past 60, 3) partner up with an 18 to 25 year old and show him that once you get up from seiza (if you can) that you can still move, 4) remain on the mat and readjust your knee brace or 5) combine 1,2,or 4. ( from the old guy in our dojo )