It could be that you are desperate on some level and they sense it in some subtle and possibly unconscious way. I I have never had this problem and have had a heap of problems of the opposite type (excellent guys want to settle down but I am not moved), so I am thinking that it might be the the issue of being desperate. If that is the case, maybe you can try hard not to act desperate and hope to fake it until you make it, as some say. The best though would be simply to not feel desperate. Can you decide that you are too young to settle down for now?

Also, a fine art of being a prick-teaser may need to be mastered by you. You might also try playing a game in which you do wear mini-skirts and issue an alluring smile periodically, but you wouldn't actually go to bed with anyone. I am not saying that you would end up being a gf, but it would be a fun game to play.

On a more serious note, you are not ready to settle down because your motivation to settle down is driven purely by your idea that you are somehow inferior to other women because men do not choose you to settle down with. And they are right - this kind of motivation would be short-lived and not enough to sustain you and a hypothetical man over a long haul. And that might also be something that men in your life sense on an intuitive level - they sense that you are a little girl who wants to play house.

In other words, perhaps your situation does not need any fixes but will change on its own as you mature as a person.