I've been on a few cruises but only on Carnival. Yes it is a younger crowd and I usually call it a booze cruise. But it's not by any means out of control drunk. There are a lot of families, but I like it because it's got a good mix of all ages just like any city. I did a 7 day western Caribbean (Jamaica, Cozumel and Grand Cayman) and I had a lot of fun. then again I was only 29 at the time and had an $800 bar bill by the time the cruise was back in port, be careful it can add up fast. If the line offers an unlimited drink option on something you normally drink it's probably a good idea to buy it. On my last cruise they had an unlimited soda pop card for $25 that I bought and gave to my kids to share. If they had an alcohol card I would have bought that one as well.
I've dine both the assigned table and times for meals option and the no assigned table or times option. The assigned table is nice in that you always have the same people at the table so you get to make some new friends. The no time or table is nice because it's just like walking into a restaurant and sitting at a private table. I now prefer the open seating arrangement.
I know more than you asked, but I love cruising.