Myself and my Mum (70) enjoyed it this week. I didn't feel it was too strenous and she coped well and even managed to climb to the top of the observation tower. Do not expect to get swimming though and we found the falls rather disappointing - we have better ones in Scotland! However the rest was great and we loved the drive to the rainforest as we got to see a lot of Puerto Rico. Just be careful not to get the two trips confused as a lot of people did and hence were disappointed.
Wendy