Question: What is the penalty for using a fake ID to get into a bar to see a concert but not buy alcohol?
Answer: Using a fake ID is a pretty severe crime, and whether you are doing so to get into a concert, buy alcohol, or otherwise misrepresent your age or identity, doesn't really matter. Arizona law punishes the conduct of misrepresenting your identity in two areas: first is the use of the fake identification to do something and second is the tampering or falsification of the actual identification card.
You could be prosecuted for a number of different crimes under Arizona law using the fake identification, including Criminal Impersonation (ARS 13-2006) and Forgery (ARS 13-2002). Both of these crimes punish people for assuming a false identity or pretending to be someone (or some age) that they are not in order to get something from the person that they are deceiving.
If you have also actually tampered with the identification yourself, you could be charged with another crime like Tampering with a Public Record (ARS 13-2407). This punishes the act of altering or changing an officially issued piece of documentation like a driver's license.
All of these crimes are felonies in Arizona. Felonies are crimes that are punished by time spent in a state prison, usually in excess of one year. Criminal Impersonation and Tampering with a Public Record are both Class 6 Felonies, which are punished by 6 months to 1 1/2 years in jail. Forgery is a much more serious crime, a Class 4 Felony, and is punished by 1 1/2 to 3 years in jail.
Needless to say, there is no reason to take such a risk just to see a band. Go buy their latest CD instead.