I'm a local to the Space Coast, and I have gone out with several different tour operators that offer bioluminescent tours on the Banana River. By far, BK Adventures is the best outfit I've gone out with.
To begin with they are friendly, helpful and informative. They took the time to make sure everyone in the group got to see comb jellyfish, as well as seeing the spots where the bioluminescence was the brightest within paddling distance. They also had patience with people who are not used to paddling a canoe or kayak, and they made sure that those folks were safe and having fun.
The night we went out, some bottlenose dolphins were relatively nearby and the guides made sure we all could see those magnificent animals. We also got to see mullet jumping. Great fun!
The trip was just long enough, but not too long. It wasn't terribly strenuous, and young and old people alike should be able to keep up with the group and enjoy the ride. All in all, it was a fun time and a great value.