Meh, don't shave for a few days and try to get a fake ID. It's worth the try.

It might be 18 to drink only... 18 for admission would be ghey, it's not a strip club.

(though naked chicks at a metalfest would rule.)
What inthezoneac said is a typical uninformed opinion of the people who don't listen to this kind of music. If you were to listen to some of it and learn about a few bands your point of view would quickly change. Satanism and anti-Christianity/religion is a common theme for many death and black metal bands, but Satanism isn't really taken seriously by the musicians 99% of the time. It's usually just newspapers and tabloids that blow everything out of proportion and make up stories of bands having sacrificed babies, virgin women, etc. A lot of Norwegian black metal bands(Scandinavia was known for many Satanic-related incidents) made claims to magazines and news reporters about being part of a sect or something just to look cool in front of their hardcore fans, just for attention and getting a little more publicity. Lyrical themes like that can be very cool if written well, but I usually prefer more down-to-earth lyrics dealing with anti-Christianity/religion or politics in a more subtle way(ie: Think mid-era Bathory or Amon Amarth, Napalm Death(political)). Still, I love all those evil spritual lyrics from bands like Morbid Angel, the decadent atmosphere the music makes is just awesome, not to mention it's heavy as fuck..