I had the lovely Denmark Christa do my dirty-work, so here is a guide to the nightlife of Copenhagen.

Nightlife
It is not easy for the youngsters to find a proper place to go out when you are about 18 years old. Most places, you need to be at least 21 to go to a club, but most bars, the limit is 18.

I know of two discothèques located in the center with an age limit of 18:

The Australian bar http://kbh.abar.dk/ contains a pool hall, dance section and live music. The opening hours is around 16:00-05:00. There are no dresscode, but will cost you a bit in entrance. Remember to bring along an ID, in case they ask for your age.
The Australian Bar
Vestergade 10c, kl.
1456 København K


If people prefer Techno / Dance music, Discotheque IN (also known as La Hacienda) is a good place for some heavy dancing and supreme quality music. There is an entrance of 150 danish kr for males and 75 for females, which is rather much, but on the other hand there is a free bar of beers and champagne all night and morning aswell. The place is open until 10 o'clock in the morning. Be aware about drugs, NEVER leave a drink without supervision. Age limit 18. http://www.discotekin.dk/LaHacienda/index.htm
La Hacienda · The Dance Floor
Nørregade 1
1165 København K



One of the BEST places in Copenhagen, if you ask me, is club Vega. http://www.vega.dk/sitecore/content/VEGA%20Natklub.aspx
Vega has an entrance fee of 60 danish kr if you go inside after 1 o'clock. If you enter between 23-01 its free. The opening hours is 23:00 - 05:00.
The place consists of several bars and dance floors according to what kind of taste you have, whether its RMB, lounge, dance, trance etc.
Vega
Enghavevej 40
1674 København V


One of the more expensive but beautiful places is the nightclub called Park. http://www.park.dk/main.asp . The music is a mix of everything.
Opening hours from 23:00 - 05:00. According to the days there are different age limits:
Thursday age limit 18, Friday age limit 20, Saturday age limit 22
Park Nightclub
Østerbrogade 79
2100 København Ø



Another trendy place at the center is the nightclub Luux. http://www.luux.dk/
It is rather expensive and only contains one dance floor, but is located just next to the metro and the subway station called Nørreport.
Age limit Friday 21 and saterday 24
Luux
Nørregade 41
1165 København K



These places are just the tip of the iceberg. There are tons of places to hang out at night.

If people prefer going to bars and café's I can recommend my favorite place called café Ludwigsen. It's a small, very cheap and cozy place with table football, pool, backgammon and a large bar. It's a mixed crowed both in age and personalities. http://www.ludwigsen.dk/
Opening hours 12:00 - 06:00. Age limit 18.
Café Ludwigsen
Vesterbrogade 113
1720 København V