Supposedly you have to be 21 to check-in to a room. It's not stated anywhere on their website or information though. I just called for a room for HRH and I'm 20 so we'll see what happens. Most people I've talked to said they don't even bother checking an ID. I plan on just showing up and looking somewhat presentable and I'm sure there won't be a problem. I believe Spaceman Spiff is/was under 21 and he has stayed there before. Bottom line I guess is don't show up with 25 loud friends and 5 cases of beer, and I'm sure you'll be fine.
Jim