Hi S/P if the girl in question knows you well and likes your nature and flirts with you that's a good start.
If you really like her go for it before someone else steps in and you then regret not doing something about it.
Keep it light and as others have said don't go declaring your undying love for her before you have even had a date or else 99% guaranteed that will put her off straight away.
You are both young and there's no rush,just let this friendship develop slowly that is if she wants to take it further, and enjoy getting to know each other on all aspects of a relationship.
If you haven't had a proper date yet( which your post implies) ask her out on a fun date nothing to heavy bowling or go karting or similar and test the ground is she even wants a relationship.
I have had loads of great male friends over the years who I have known well and mutual flirting has happened but I wasn't looking for a relationship with them,it was light fun banter and a good mutual flirt does boost both male and female egos.
I wish you well and keep us informed and remember if this girl doesn't want a relationship with you respect her decision and keep the friendship if you can, good friends can be hard to come by x