It would be illegal for an attorney to answer this question. When you tell us that you're going to commit a crime, rather than that you have committed a crime, we're not allowed to help you commit the crime.
While I agree with Mr. Loncar that it's unethical for an attorney to advise you about how to commit a crime, I'm going to make a few assumptions here that what you are planning to do may not be a crime.
Unfortunately, many venues that serve alcohol and have concerts or live performances restrict the attendance to 21+. Assuming that you don't try to purchase alcohol if you get in, and you are planning to use a "fake id", in most instances, the worst that could happen is that the bouncer will confiscate your fake id or ticket and you'll be out the ticket price and fake id.
Yes, it's probably a crime to use or possess a fake id, but even in this era of "homeland security" it's not a huge crime and the cops are more interested in people who are making ids and profiting from them rather than using one.
If the venue confiscates your id and ticket, rarely do they bother calling the cops. Just don't have any other illegal substances on your person or in your backpack or pockets, if you know what I mean, then there could be problems if police get involved...they're way more interested in that kind of bust that could stick.
And if it does become, worst case, a police matter, you can usually get the charges dismissed or pled down to something that won't be a criminal record. Just don't sass the bouncer if you're caught and things should be OK. Not sure what the law is in CA, but usually alcohol possession alone by a minor where a DUI isn't involved is just a ticketable offense with a small fine.
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Don't do it. You could be charged with a misdemeanor, like some minors we recently represented who were caught with fake IDs at the Coachella Valley music festival. We got the cases diverted, after the defendants took some classes, but we had to negotiate with the prosecution first.