The older I get (and I turn 66 on Friday April 6, so I know what old is), the more I see protecting your joints as crucial.  Muscle can be built, even tendons and ligaments can be gradually strengthened, but the joints are in need of maintenance which they rarely get!  When we are young, we literally take our joints for granted, and beat them up exercising to build muscle, compete in sports, and otherwise propel our bodies around. 
 
This is all fine, but it points out the old adage that ‘youth is wasted on the young’.  If I was young again, I would do what I do now:  first thing upon rising in the morning, I put my ALL of my major joints through a brief warmup.  I do it right in the bathroom, so as not to disturb my wife.  (I am an early riser). 
I start with just stretching my arms upwards, as high as I can, one arm after another.  I rotate my head on my neck each way similarly.  Then, I put my hands on my hips, and rotate a few times in each direction for the hip joint.  4 to 5 reps, easily, just to get the synovial fluid going in the joints. 
 
Next I put my hands of my knees, and rotate them in each direction.  Then, I do the same for my elbow joints and wrist joints (I do them at the same time), elbow joints, shoulder and hips together, one quarter squats, and another easy twisting motion.  This whole thing takes maybe 2 or 3 minutes- I will post a video to show you how it’s done.  Easy to show, hard to describe.
 
The beauty of this is not only does it start your joints with an easy warmup, it also wakes you completely up from head to toe!  No more groggy mornings until you get your coffee. 
 
I used to lift heavy weights, and now realize that was a mistake- especially for the joints!  Lifting later at a really slow cadence (Superslow ala Ken Hutchins) was a huge improvement, but still too much, and unnecessary.  The weights were less, but still damaging to the joints. 
 
Now, and for well over a decade, I do bodyweight exercise along with isometrics and ‘virtual resistance’, which is putting the body through a self-resisted protocol of complete motion.  The resistance is self generated in this, and is the key to not only building and maintaining muscle, but also in rehabbing damaged joints from sports and weight lifting injuries.  It took me a little while, but now my joints are perfectly healthy, with all of my knee and shoulder joint injuries healed!  You can do this as well.
 
The other key thing I recommend doing daily is stretching, methodically.  It doesn’t have to be yoga, but gentle stretching is essential for your health!  You need to get on the floor, and I do it mid-way in my morning workout.  I don’t want to explain it in words, but again will include a video.