19!
Seriously... how do you quantify wanting?
Somewhere between how much someone walking around outside wants to find a $5 bill on the ground vs. how much a 6-year-old kid wants a bunch of Christmas presents under the tree on Christmas morning, I guess. Depends on the chick.
A girl wanting to be approached is like you wanting a [some food you like]. Sometimes you want it, sometimes you don't.
Let's say you like apples. If someone approached you and handed you an apple, and you had just been staring at this person and all the apples in his cart, you might say, "Oh man, thank you! I was just wanting to eat an apple!" while at other times you might say, "Very kind of you, but my hands are full and I'm not hungry."
Then you get into stuff like how cool is the guy doing the approaching, how smooth is the approach, etc. Some scary-looking guy jumping out of an alleyway and shoving an apple in your face is probably not going to be very welcome, even if you were kind of hungry. Some guy chucking apples at you from across the street is also not welcome. Thus why most women don't like men startling them to approach or cat-calling them from far away...
A weird guy wanting to give you an apple will just freak you out, EVEN IF you are hungry.
A super cool, high status guy wanting to give you an apple will make you feel good even if you're not hungry right now or you already have an apple tree at home (e.g., women in relationships).
Etc., etc.
Chase