Probably because the venue serves alcohol, and 21 is the legal age to purchase alcohol in the US of A.
Although if you take a look at the schedule on
ther website :
<blockquote>Friday 03.11.11
The Mighty Heard, Mello D and the Rados, Navi and the Whole Damn Delegation
Doors 9pm/Show 10pm/
21+/$8
Saturday 03.12.11
Kohoutek, Luger (Spanish psych), Caves Caverns, PJB (aka Psychedelic Jam Band)
Doors 9pm/Show 10pm/
21+/$8
Monday 03.14.11
The Alliance Francais presents: Chateau Marmont
$10 in advance, $15 at the door
Thursday 03.17.11
Immanent Voiceless, Keep, Samuel Joseph Kim
Doors 7:30pm/Show 9pm/
21+/$8
Friday 03.18.11
Dark Sea Dream, 28 Degrees Taurus, Night and the City, Phonic Riot
Doors 9pm/Show 10pm/
21+/$8
Thursday 03.24.11
Foul Swoops, Teen Mom
Doors 7:30pm/Show 9pm/
21+/$7</blockquote>
All the dates say 21+ except for the CM date, so that
might mean the age limit is lower for that show.
Someone would have to contact the place to confirm, I guess.