Yes, surely you will be able to get in. I am also 16 and American and i'm going to Spain this summer. My friends that live there (17-18 years old) are sure that I will get in. Also, if you walk in with a boy on your arm (or something) they will most likely let you in. My friends don't seem concerned that I won't be able to get in, so you should also be fine.
I have no idea about the alcohol, sorry. However, i'm sure it wouldn't be EXTREMELY hard to get if you really wanted it.
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descubrete, muestrate a le gente como eres sin mascara