We find this climbing stuff really hard at our age, but around CO, we have very few grades above 7% that are paved, our challenge is those long grades at 9000 ft elevation or higher, we (I) can stand, if need be for the short pulls, but staying seated is really mandatory at altitude, one just runs out of oxygen and you beat yourself up standing too much, especially on the tandem. Rest stops are part of the ride! We did do a tandem ride two years ago, and while we were grinding away up a long 6% above tree line, some young buck (and his doe) pulled right by us with a 30-28 gearing, their cadence was slow and he was complaining, but they outdid us!
R&J