Can I come in, pay some admission and just listen to music and not drink if I’m 18+? Some bars where I’m from, Peoria, IL bars just mark the 18+ hand.

Not at Smartbar. The liability & responsibility is too much of a hassle. Just grow up.

All the shows I've gone to they check IDs at the door and don't offer wristbands to distinguish between 21+ and 18+. I'm fairly certain you're out of luck on this one. At other venues, however, they sometimes have 18+ shows with wristbands. Check the show specific marketing to make sure, but I'd assume everything is 21+ here.