Let me give you a little advice, my young friend. The only thing most teen girls know about music(if they are not musicians themselves) is if the guys are cute.

As a former teenager myself, the only reality of impressing a girl with the fact of you playing guitar is seeing or hearing you actually play it.

(And nobody likes that guy who brings his acoustic guitar unasked to a party and start playing it to impress the girls LOL)

The best strategy you can employ, is to have the guitar lying casually in sight in a corner and if they happen to ask about it, you can say it's yours. And hope you know a cute, romantic teeny girl song. I know you like Beatles, but that won't get you anywhere with today's girls. If you wanna get em excited learn a stupid Justin Beiber song or something similar by Justin Timberlake or something.

The others have well commented on the the fact that they won't know or care if a song is in a certain key, what chords are used or how many sharps or flats are in the scale.

I was one of the best guitarists around back in my teen years. And I played a few times at school in our TV studio and at a party or two. It never once got me laid or anything close to getting laid.

All it got me was guy friends who were musicians.