Explorer Auckland to Dunedin

[silkismom]

We just discovered this sailing and are very interested in it for our 55 anniversary in Dec 2020. My main questions is:  how much "explorer" will this be, we have done zodiacs in Galapagos. I've seen posts with people complaining about people "not fit enough" for exploration cruises. We are a little slower than we used to be, no running anymore, but usually will get there, eventually.  Thanks for guidance. We don't plan to book this until Sept.