Is she also a high school student, about the same age, also a part time worker? Then I think this could be appropriate, and you're at the same "place" in life.
Here's why it might be a problem for your boss:
If your training or employee handbook forbids coworkers dating. Think back about whether this was part of your training. Maybe even ask your boss if there would be a problem with you asking out another employee.
If you don't take "no" for an answer. If she says something like "Maybe," then the ball is in her court to follow up--take it as a no, and you'll be pleasantly surprised if she does follow up. (See script below.)
If it causes "drama" somehow, like the coworker avoids you afterwards, or her ex is also working there, or you two end up making out all the time instead of working. If you're pretty good at focusing on your job, and so is your coworker, then there's probably a low chance of this being a problem.
Try a script like this:
"Hey, I don't know what your work schedule's like, but would you like to go see [movie] with me on Friday night?"
She might say yes, possibly with a counterproposal ("already saw that, but we could see [other movie] on Saturday.")
She might say, "You mean like a date?"
- And you can say, "Yes. I don't know you very well yet, but I would like to go on a date with you. No pressure to say yes -- I know it might be weird because we work together."
Or, she might say "Maybe" or "I can't make it" or something.
- Your response: "Well, please let me know if you ever want to hang out. I wasn't sure whether to ask in the first place because we work together, and I know that might feel weird, so no pressure."
Note about this script: when you bring up that it might be weird because you work together, this has 2 main functions:
- It convinces her that you know you should not be "creepy" about this and that you will respect what she wants.
- It gives her a gentle way to decline if she's not interested.
She can still legitimately say she doesn't want to date you as a coworker, as the main reason not to date you or as an excuse, even if she has dated a coworker in the past or if she does in the future.
Think of dating a coworker as costing you something: for instance, it could be annoying or awkward if it doesn't work out or it might make your boss mad. So you should be a little more careful about asking out a coworker than someone you met in another way. (And you're thinking about that--that's why you asked the question!) The same is true for her, though. She might be willing to take a risk to date a coworker she has a huge crush on, but not to date someone she doesn't know well.