Hello Kalifa,
Don't worry, there should be all ages on the Panama Canal cruises ('mature' fellow passengers are often very interesting with lots of different life experiences). We were on the Island Princess in Oct 2011 and we loved it.... and the ports as well. Even in Aruba, I enjoyed the snorkeling (husband remained on the boat). Cartagena, we walked out to the entrance into the cruise port, where there are several private tour operators wanting your business; do your homework as to what you want to see, take others with you as they like to fill their mini-vans, they'll take you where you want to go, but above all, don't pay the first asking price, haggle a bit! Our guy took us to an emerald business, which I now regret not buying in (I later found out they were very reasonable, as off the beaten tourist track, and a bona fide business), then he took us to the fortress and the old town where we walked around for 45 minutes, would have liked longer than that. As for the Canal itself, if you really want the full experience, take the excursion boat tour that leaves from Lake Gatun after your ship traverses the first few locks.... and go all the way through to the Pacific, then back to the ship by bus. We really enjoyed that! In Costa Rica we went on a privately arranged tour, John Joyner Tours.... he was very good, and took our minivan group up to the rainforest national park with an outstanding zip line.... 12 stations over the jungle canopy, it was breathtaking, a fabulous experience (and we are early 70's but obviously very active!!). In Jamaica, we did the ship excursion to the sugar plantation, lovely place, lovely lunch, peaceful but interesting and away from the crowds. It is near Falmouth, so a ways from Ocho Rios, but the drive gave us other perspectives on Jamaica also.....
Have fun! We plan to do this cruise again in a year or two, we liked it so much.