A 60 mile ride on flat roads at a leisurely pace of 12mph would take about 5 hours. College cyclists ride at 20-25 mph. Pros ride at 30+. On my weekend rides were I average 19mph on the flats I regularly get passed by some very old riders. The point is: 100km a day is a difficult but achievable goal for a reasonably fit 70 year old.
I am 52, and I do 27 miles each Saturday on a longboard. It takes around 2:20 to do it. When I am 70 I may not be on the longboard for those distances, but no problem on abike i'd bet.
