Taking the assumptions that the 21+ drinking restriction is the a part of the problem, is there a space that a music venue is similar to, but differs in regards to drinking?
A music venue is like a sports stadium.
Both are spaces in which live performances take place. Spectators are people of all ages, including youth of all ages. Alcohol is present and flowing (almost) freely.
Innings = baseball
Sets = music
People can (usually) come and go from their seats during game and move around the stadium, just like people can come and go from the showroom and venue during a show.
Perhaps an in-depth study can indicate there the differences are in practice between these two and how we can learn from stadiums to change policy on music.
About the teen dance ordinate of Seattle.