The only person who needs to be 21 is the person checking in, they don't care who stays in your room with you. The thing to be wary of is noise. To avoid this, stay into places that cater to younger people. The other thing is all the clubs are going to check ID, so that might cause problems. The best places for young people to party in Vegas are off the strip: Hard Rock & Palms are both hotels that cater to people in their 20s. Cabs are everywhere in Vegas, so getting around to the Strip won't be an issue and during the day, the Palms has a shuttle. On the strip, I would check out MGM, New York New York, Treasure Island, and the Venetian. The very last one is pricey but all the rooms are suites and you can easily split it up between a lot of people. The Venetian also has Tao nightclub which you might be interested in. Luxor has the Cathouse club which I like and also LAX, which is fairly new. Ceasar's Palace is also a little older, but they have the club PURE and lots of interesting people. I would avoid downtown, or hotels like excalibur and circus circus. Good luck and have fun! :)