Why did you give her flowers? If it was for her birthday or something she may have just thought it was sweet, something traditional that might be expected from an older man. She may have not appreciated them but been too polite to express it - many people are taught to not complain about being given a gift.

Your idea of her flirting? Eyes sparkling and being playful? That isn't flirting. Maybe it was when you were twenty, but it isn't now. Chatting in Facebook and going to a coffee shop are also in no way viewed as flirting.

You're right when you say you aren't in high school anymore. But she was in high school not that long ago. You are old enough to have been 40 when she was born, which although it's becoming more common it's still an older age to become a parent.

Most people aren't expecting or prepared to handle romantic interest from someone who is probably older than their parents - she would have just seen you as a sweet older man. Her distancing from you now is probably a sign that she has picked up on it and is uncomfortable.

Like others have said - join a dating site. Look for women closer to your age. Stop interacting with women so much younger than you because they are very very unlikely to reciprocate or even notice your intentions because it is so far out of their normal experiences.