Check sites like Cruisecritics.com for more information about the cruise itself.
And do a check online for Cruise Scams

You didn't win anything.. there are expenses as well as timeshares attached.

If you are looking for a cruiseline that is "Youth" friendly then most of them will have families and children on them, unless you book during off season when school is in session, but there will always be children on the ships, just not as many.

The most active cruiselines for your age group would be Royal Caribbean, Carnival and NCL. You will find more older adults on Celebrity and Holland America, but there are pretty much all ages on most of the mainstream lines.

I would suggest that you look at the three mainstream lines websites: http://www.ncl.com , http://www.carnival.com, and http://www.royalcarbbean.com to get an idea of what itineraries are offered and what length of cruise is offered. Either that or contact a cruise specialist agent to ask these questions. They are trained in all the different lines and will be best able to qualify you to the best line based on your answers to questions they will ask.

My recommendation:
Royal Caribbean offers many things on the ship for all age groups. They have the rock climbing walls, the newest ships have the flow rider, there is also mini golf, pools, games etc.

Carnival offers quite a bit of activities for your age group, and if you are planning on a 3 or 4 night cruise, you will find more people your age on the ship…remember they were once known as the "party" ship. But they are catering more to families now..but again, book in off season (not summer, spring break or Christmas time) and you will find less children on the ship.

NCL offers a bowling ally on their newer ships, along with a variety of other activites to participate in, there are plenty of activities for your age group.

Also, the cruiseline you decide on would be dependant on how much money you want to invest in your cruise.

Good luck in your choices.

On the Disney Magic, the Mickey pool has a separate filtration system. Non-potty trained children are allowed in this area since it can be easily emptied, cleaned and filled if there is a diaper accident.

On the Disney Wonder, toddlers can enjoy Mickey's Splash Zone, a 385-square-foot play area with interactive fountains.

Assuming you are going with parents or someone at least 21, I suggest Carnival. You are not going to be able to buy alcoholic drinks on board, though. They are very strict about that. In the Caribbean countries, you can drink at 18, but do not miss the ship by drinking too much. The ship does not wait beyond the scheduled departure time for anyone – except maybe the Captain.

Personally, I would suggest you and your friend go to an all-inclusive resort in Dominican Republic. They have good beaches, good fun at the resorts, and no problem doing all the drinking you want. Everything is included at one price.