We are in our 40s and 50s. We are taking Celebrity's Zenith on 12-22. Our friends are in their forties and they are going too. Generally longer cruise have slightly older crowds. The older people have more time off and a little more extra cash to spend.
Also most of the South America cruises have a large portion of customers from Brazil, Argentina and Chile. Many of them like to dine late and enjoy the active nightlife, dancing etc.
I have been on the Norwegian Dream, as have my friends. We chose the Zenith instead because of the better food and service. The prices were very comparable.
We would probably not go on the Dream again unless the prices were so staggeringly low that we couldn't refuse.