Hate to ruin the fun, I'll step in and comment not to expect a huge amount of teens on this sailing. Couple of reasons; first, its 8 days. Not everyone gets the whole week off, and the likelihood of cruising for 8 days over thanksgiving is less than cruising at all.
The general consensus I have seen among my cruise friends is that Thanksgiving cruises are probably less populated than other cruises during "on-season"
Don't fret too much, because it could be different, but given the current state of the economy, be prepared if there aren't too many people onboard either. Especially when you consider that the 3rd business quarter for the cruise industry was a huge slump. RCI -44% profit over a year ago, and while CCL fared better, it still gives a feel for the state of the industry.