Trixie, you think too much for GFY. You and I should go start a board somewhere together and invite KCat and some other smart people.
As for the question, I don't think it's an age thing. It's more of an attitude or "feeling" the guy gives off. Like Trixie said, it's a mixture of body language, mannerisms, type of humour, eye contact, and things like that.
For instance, if a woman is sitting on an otherwise empty bus stop bench, she will most likely sit on an end, not in the middle. A guy coming up SHOULD sit on the other end, but if he's pushy, he'll sit in the middle, next to her. That's just creepy and very threatening. So it's things like that.