You know...I forgot how old you said you are. But keep in mind that many girls her age have unhealthy relationships with men their own age. Several of them deserve to be with older men and could handle it much better than many may think. She's probably more mature than you give her credit for and she can probably handle you and what you want better than you think she could. Also, there is a chance that she thinks about you the same way that you think of her. Maybe you should quit being so reluctant to actually let someone in and give her a chance. Maybe it would be good for the two of you. You will never know if your chemistry will lead you to nothing more than great sex, or a loving relationship.
Just my two cents, if that makes any difference.