Getting old--it creeps up on you.  On silent feet.  You're doing great one day, then a knee is not so great, then the other one.  And you're walking slower.  The thing to do is not give in.  That first knee--don't wait.  Leap right on it to fix it--wear knee pads at all times, find out what vitamins will help it, etc.  Ask people--you'd be surprised how many people have good ideas about body fixes.  Like for arthritis, especially a mild case, vitamin D (at least 3000 unit a day) taken with Calcium/Magnesium will handle any pain.  Now, you've got to know, natural things like vitamins are MUCH better for you in the long run than aspirin or any other pain killer.