To just hang out at the bar is 21+. Concerts and dance parties have their own specific age restrictions. Most events seem to be 18+, but if there is a show you really want to see as a 16-year old parental accompaniment might be permitted. Best to have your parents call and ask. Clubs in DC are asked to abide by curfew laws, meaning many teenagers can't legally be there after a certain hour without a guardian.
No.
I believe each event has its own restrictions. The show I attended was 18+
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