Underage girl flirting with me at work?

A 17 year old girl is flirting with me at work. She is pretty, yet she is smart and mature for her age. She goes out to concerts and has her own friends, but isn't very flirty towards others, but me. She also took many AP classes last year. While I admire her and am falling in love with her, she is 17, and in the USA, it is illegal to date or have sex with a minor (under 18). What should I do to let her down gently and/or wait until she is 18 (next May)? I do NOT want a minor mistake to mess me up for life.
Underage girl flirting with me at work?
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