Been to CTI and CSS so can only speak of those. CTI is a high-rise resort on a smaller property where CSS is spread out and requires some going up and down stairs. Both are informal and relaxed with great food and staff. CTI does offer a catamaran cruise and horseback riding while CSS doesn't. CSS offers a large property where you can get away and enjoy some romantic strolls. My wife and I are in our latter 40's and enjoyed CSS more...maybe it's because we were married there, but we spent our anniversary there last year and will again this year. The best thing to do is look over all the info on each property and go where your heart takes you. No matter where you go you won't go wrong.
Based on your comment about informality, I would eliminate CSA, not that anything in Jamaica is truly "formal". With regard to the others, you will enjoy any of them.
My opinion: CSS is most known for its lush landscape. CTI and CN both have a more active crowd (but that can change depending on who happens to be there). The reverse of that is if you are looking for more alone time, I would lean to CSS. CN has the nicest beach of the three. CTI has the most privacy if you want to go "au naturel". All three have excellent food. For those of us who have been going to Couples for a long time, CTI holds a special place in our hearts because it was the first.
Hopefully that gives you some idea of the differences, but let me assure you, whichever one you select, you WILL ENJOY IT.
Ahh, the age old question, "Which one is best"? The truth is, there is no "best". Really. Each resort will give you something different. Different food, entertainment, activities, yada yada yada. However, one thing will be the same regardless of where you are. The service. The staff at each resort will make you feel welcomed. They will take care of any difficulty that may arise. Remember, in Jamaica, there is "No problem". By the end of the second day of your stay, you will have made friends with complete strangers and those relations may last for years. You will be smiling almost all the time, and throughout the day, you will greet and be greeted by the staff.
Couples is not just a destination for a "vacation". No, it's much more than that. And as they say, "Once you go,you will know".
As to your question. One thing you will find, is that there is no age barrier. Young people in their twenty's to those of us who have just a bit of mileage on them.
Here is how to find the one Couples resort that will suit your needs. Decide what it is you would like to do while there. Then check out each virtual tour on the home page. As hundreds have found before, one of those resorts will "call to you". Trust your instincts. If there are specific things you would like to know about any of the four spots, ask away. There is no shortage of people who will answer your query.
By the way, welcome to the Couples family. Even though you haven't even gone yet.
We are 56 and 57 (two more weeks and I will be 57 also!!!). We just booked our 4th trip to CSA. CSA is not glitzy or formal - just tropical and comfortable! Everything you need or want is there. You can be very active with all of the included activities (we scuba dive) or you can just enjoy the beautiful beach or one of the pools. We like CSA because you can be as active or inactive as you choose to be. We haven't tried any of the other Couples resorts because we love CSA so much. I am afraid we would just compare. Whichever one you choose, I am sure you will be happy.