Hi Bob,
It looks like such an amazing trip doesn't it?!
We had one departure in March 2015, but after the earthquake we decided to cancel the dates for the remainder of 2015 and the whole of 2016. In regards to the difficultly of the walks, a moderate level of fitness is required as you could be walking for over 5 hours some days, which may be quite strenuous. Some walks will include steep uphill walks and rough ground - just bare this in mind.
There was someone in their mid-70's on the March 2015 trip, so it's certainly doable for all ages.
Kindest regards,
Monty