You can’t teach old dogs new tricks.  Is it true?
 
Well, I have found that teaching adults new skills isn’t too difficult.  The difficulty comes in changing an old habit.  Changing an awkward grip, changing a stroke, or changing a footwork movement takes time and persistence from both the coach and player.  On the flip side, a new serve or a new serve return technique or a new looping variation can be learned fairly quickly for these same players.