We did it last July and had a great time. It IS strenuous, so if you're not in basically good shape you may have a bit of a tough time. We saw a young woman who was doing it with a young (preteen boy), both of whom had never kayaked before and they seemed to be struggling a bit but the guides were very patient and helpful. I would say that as long as at least one person in your boat (the kayaks seat two) has strong arms and has any experience at all with a small boat, you'll do fine.
Our group included my 78-year-old dad and my 15-year-old nephew, both of whom enjoyed the excursion, as well as 40-something me and 50-something DH. One nice treat was the mini-candy bars they gave out after we snorkeled, to get that yucky salty taste out of our mouths! (FYI, you don't HAVE to snorkel on this excursion; if you prefer, you can walk around an interesting rocky beach/lagoon area.
Hope you have fun--