This is the review that we did in 2003. I don't know how much (if any) it's changed...but hopefully this will give you a starting point.

Hope you guys have fun!! Ginny
We enjoyed the Rhino rider and snorkeling excursion. You have a brief van ride to the lagoon, where you receive basic safety instructions and learn the "ground rules" for the excursion. The tour leaders advise you to slather on the sunblock and then you pop all your stuff in communal lockers. You then get your snorkeling equipment and a life jacket. The rhino rider holds two passengers and I believe they will pair you up with someone if you are by yourself.
The tour starts out in a structured manner, meaning that there are several stops (your guide will point out little trivia bits about the island and the people who live there). There is also a photo taken as you come out from underneath the bridge. Once you reach the snorkeling area, the rhino riders are tied together and you have about 45 minutes or so to swim, snorkeling or relax. Soft drinks and bottled water are available (free).
On the way back to the dock our tour guide told us that as long as we kept him in between us and the shore that we didn't have to follow in a straight line...until we reached the area approaching the bridge (a NO wake area)...after that we would have to follow in a straight line. This is due to the numerous shipwrecks that are at the bottom of the harbour.
We returned to the dock, checked out our picture (cute, but expensive) and boarded the van for a ride back to the dock.
There were several parent/child and parent/teen combos on our excursion. Active senior citizens would probably enjoy the excursion, but beware you are on a "wave-runner" type boat...depending on how choppy the water is...it could be a VERY bumpy ride! Everybody on our excursion seemed to have alot of fun.