I Need advice on how to talk to someone not knowing age?

There is a girl in my mall's Bubble Tea Shop, however I do not know her age and I am in my 20's. I do not want to look like a creep so I am not sure how to approach this situation, if it was a common workplace like a School or a Job I would feel more confident.

Also since I am customer and she is working I feel this makes the environment more complex. I can't just hold the line to talk to them and I do not want to look weird waiting to just talk to them with no one is around. I would normally pass up on a situation like this but I feel like trying to talk to them. I just need help on how to go about it.

I Need advice on how to talk to someone not knowing age?
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