Fiji- Blue Lagoon, Octopus, or Nanuya?

We will have 5 nights in Fiji. We are a retired couple in their 60s. Not looking for night life or having a lot of children around. We will need to learn how to kayak and snorkel. After reading reviews and websites we are leaning towards Nanuya because we can eat when we want to and no children under 7 allowed. We will want to take a boat trip to the caves and since this will be our only island splurge we want it to be nice. What do you recommend?

We have stayed on both Octopus and Nanuya, but not at Blue Lagoon..
Both are great, but your preferences strongly suggest that Nanuya would be best for you.
Book early, they are often full.
Say "Hi" to Lance and his Mum from Peter & Margaret.

Cheers,
Peter