I think what you look like or your age has nothing to do with it in most cases seems most predators look for opportunity and a vulnerable female or male ; best thing is don't give them opportunity and if you have a means of self defense be ready and willing to use it and let them know you ARE prepared to fight if need be
I agree with this.
Predators look for a (easy) prey, they don't want to get hurt, they don't want to get caught, they don't want a duel, like in movies, against another male. They just want to want to "dominate" someone they regard as weaker then them. Proving them that who they regarded as a "prey" is not a prey, but can fight back, more often than not it disrupts their mental state (predator - prey) and may open a window for getting out of dodge. In other words it creates a surprise effect.
I can't say what can be the most effective tool to achieve that, as it depends on age, gender, level of fitness, training, mental state and so on. But a pepper spray kept in a deep pocket or in a bum bag is useless; a blunt or sharp object used for defense without proper training can become very dangerous for the user; a whistle or a rape alarm may be ignored by most people; unless you are a very fast runner, running away from a predator (not incapacitated) may be pointless.
I think everyone has to find the right solutions for themselves, eventually with a help of a (serious) professional, and not to feel afraid or shamed of saying "I am afraid". For me "fear" is what it keeps me from stepping over the edge of a cliff, crossing a road without looking for incoming cars, picking up things from a hot oven without protections and so on. In other words "fear" (in the right amount and processed) is what makes me take steps to be prepared and feel safe.
Just my two cents.