As A 21 year old girl who frequently cruises with family and friends I thought it would be interesting to hear A review from someone who isn't exactly on a cruise to gain knowledge about the port or ship, but is there to have fun with family and friends, relax and party.
The only two cruise lines I have traveled with is Carnival and Royal Caribbean. Personally, I prefer Carnival. For any family traveling with teens and young adults, Carnival is more fun. The staff and cruise line in general is more laid back and less strict when it comes to allowing teens into the casino and clubs past a certain time at night. When I was 14 I took a carnival cruise (Carnival Legend) and played in the casino and got into the club past the "teen" hours. The same thing happened when I was on A carnival cruise when I was 16 (Carnival Victory). I looked older then I was, so maybe that helped get me in, but if you look really young, they'll ask for proof of age. Often times, me and my friend would walk in with people we met that were older and they never questioned us.
On Royal Caribbean I had just turned 18 and went with a friend who wasn't turning 18 for another two months. They gave her a hard time about going into the nightclub during the "adult" hours (past 11 pm I believe). To get around this, I would stand next to the guard and talk to them to distract them while we snuck her past security. It was so easy to get in if you look old enough. Royal Caribbean punches holes in your room key, 2 holes if your under 21 and 1 if your over 21. Thats how they no if you can order drinks, so unless someone else is putting the tab on their card, its really hard to get drinks.
Although Royal Caribbean is known for their bigger than life ships, I find carnival to be an overall better cruise. The food is amazing and there is no shortage of fun. On the cruises I've been on both lines seem to have many young adults but carnival truely is more of a "fun ship"