Well, the girl I've sorta kind of been eyeing, talking to and "crushing" on for a long time, I've been doing so for I'd say...actually 4 years now too.
But the reason I haven't said anything, and neither has she to anyone else, is because we're only now finishing high school and because she's said that she doesn't want to date until she's ready for a full-time commitment, seeking marriage, and already established in college, likely. I'm the same way.
If we end up going to the same college, and I get to spend more time with her (right now and throughout high school, we've been so busy with schoolwork we hardly spend real time together. She's in the top 1% of her graduating class with a 4.5 GPA, as well, so she's been busy), then I might ask her out.