Are you sure that they are flirting with you, maybe you are mistaken.
However, if they are flirting with you, it's because you are attractive. Just because a man is older, and married, his animal instinct of attraction doesn't disappear. When he sees an attractive woman, he is compelled to speak to her, and interact with her. He derives pleasure through the interaction, even if he knows it will not lead to sex, or a relationship.
You attract older men for the same reasons you attract men of any age, because you're hot!
One day, when you're 15 years older than you are now, and guys don't give you this kind of attention, you'll recall how nice it was to be wanted.
As for then not doing it as often when you're parents are in the room, I think it's because your parents being there ruins the atmosphere, and makes it less pleasurable for them, plus they don't want your parents to think they're creepy.