Having trained pretty much my entire life in martial arts, specifically for self-defense, the one thing that needs to be acknowledged is the process that one goes through (or should go through) when facing threatening situations.
The process itself is quite involved, but its essence is simple: you start off with non-physical methods (talking, use of body language, use of command voice), progress to defensive maneuvers only, and finally engage in full-on offensive techniques.
Each scenario you encounter will require a different response, and only through training and experience will you be able to deploy these methods correctly.
The alternative is what probably 95% of the population does: freeze, tremble in fear and give in to the aggressor.
As seniors we usually have a tough time using physical skills against a much younger opponent, so we should probably practice the earlier stages of defense - talking, etc.