You'll get served. Don't worry.
I've been to Bacelona 3 times. It's an OK place. I recommend Lloret or Tossa de Mar for a day trip.
Enjoy.
If you're with your parents, you'll definitely be able to drink alcohol don't worry. Just don't drink too much and get really drunk - otherwise it'll be fine! I recommend going to IceBarcelona in the Olympic Port for amazing cocktails in a bar that's surrounded by ice!
The laws in Spain make t so your Parents may buy you a glass at dinner.
I'm going to Barcelona on holiday with my parents and I'm 17 years old and will only be 3 months away from being 18 when I am there. My parents will be taking me to restaurants and wine tasting and I didnt know whether I would get served or not? I get served in England without id but I live in Newcastle so its not hard. Just need to know I wont get kicked out :P
Thanks