It's called "the art of self-defense" for a reason

No matter what martial art you have studied or plan to study, one rule stands above all the rest: you're learning a highly refined art of self-defense.  The key word is "defense."  Never, under any circumstances, are the techniques you've learned to be used as offensive weapons. 
     Because so many young children are studying the martial arts these days, teachers from coast to coast are continually driving home the message that bullying others is forbidden.  The discipline of learning a martial art must carry over into life outside the training hall, and you must never use what you have learned in order to be the aggressor.  To do so would violate the most fundamental tenet of the martial arts. 
     But if you're 60 or 70 or older, the same rule applies.  If you're an active martial artist at, say, age 65, you're undoubtedly in better shape than most people your age, and you have acquired a body of knowledge that enables you to do some damage to an opponent.  You have also learned that modesty, restraint, and respect for your martial art require you to use what you know only for self-defense purposes . . . and then only if you can't walk or talk your way out of trouble.
     The higher your rank, the more humility you should possess.  This means, in part, not worrying about "losing face" by walking away from a tough-talking bigmouth.  Whenever you can walk or talk yourself out of a confrontation, that's the right thing to do.  "So why did I go through all these years of training?" you ask.  Simple.  No matter how much you seek to avoid conflict, you always run the risk of coming face to face with a situation that requires action.  And if the punch is coming toward your face, you need to respond quickly, as noted in my recent three-part "DO SOMETHING" posts. 
     Precisely how you respond to an actual attack depends upon two things.  The first is your psychological preparedness to defend yourself.  You need to KNOW, not just think, that you will not allow yourself to become a punching bag in the event of an assault.  The second is the depth of your martial-arts training.  Attaining a black belt does not guarantee that you can whip anyone who attacks you, but it certainly indicates that you will respond automatically when a fist or foot is flying in your direction.  The longer you train, the more automatic your responses become.  This is why a professional martial-arts school is vital to your development.  You will train with other students and learn what it's like to block actual punches and actual kicks under a controlled situation.  You can read about these things, but you'll never know what an attack is like until a fellow student actually attacks you under the watchful eye of a master instructor.
     If you have "retired" from your martial art or are just beginning to think about enrolling in a class, it's time to get moving.  The fitness benefits of martial-arts training are huge and well documented.  And the self-defense knowledge that comes with ongoing training can help keep you out of harm's way.
     Find a senior-friendly school near you.  Ask to watch a class before you decide to join.  And listen for words like, "This is all about DEFENSE."  A professional school is never a training school for bullies.