Just because you're 18 doesn't mean you can't work at a bar - there are plenty of jobs that don't involve serving drinks. You could work as a barback, which means you'd be responsible for restocking supplies, cleaning up, and generally helping out behind the bar. Or, you could work as a food server if the bar serves food.
Think of it like working at a restaurant - there are lots of different roles, from host/hostess to server to bartender, and each one has its own set of responsibilities. At a bar, you might not be able to serve drinks, but you can still have a blast working with the team and making sure customers have a great time.
Everything You Need to Know About Working at a Bar: Skills
