Never
. Honestly, I've never even been asked by someone I was interested in. The first time I was asked outright was when I was 15, and I really did kind of like the guy, but I felt he was too pushy to get serious and physical, which I was in NO WAY ready for. I refused. I was asked again just a few months ago, and it was definitely a heady experience. He was quite popular and had a lot of girls trying to get his attention. I really did not care for him because he was arrogant and had a dark, sometimes sexual sense of humor which I was not comfortable with. Looking back, he was probably only interested in me because I was hard to get anyway.
So for you other teens who might be reading this, please know you're not some sort of freak if you've never been on a date, and that it IS ok to refuse if you're not comfortable with the person for whatever reason.