There is also a lot to be learned on the
'crazy guy on a bike' touring site.
On my bike tours riding with around 65 pounds of gear I needed at least a 34 cog on my cassette and a 24 small ring on the crank.
I was in your age range then and not a particularly strong rider so I was glad to have
that low gearing to spin over the Sierra's in California and the Rockie's in Colorado and Wyoming and other states.
Nothing wrong with walking up some sections as mentioned and it can be a nice change of pace depending on if one's shoes are comfortable for walking.
However I found I preferred spinning up steep sections of mountain passes even if it was only at a 4 to 5 mph pace.
Later I actually switched to a crankset with 22 small ring.
I like having that low gearing as an option.
Some of those passes and hills go upwards for a long distance.
My friend that I accompanied on two tours was a much stronger rider and got by fine with a 32 cassette cog in back and a 24 or 26 small ring on his crank. I forget which.
If I tried it again being a decade older I'd do a 36 cassette big cog and a 22 small ring on crank for insurance.
As they say 'your mileage may vary'. YMMV.
Factors of one's fitness level, knee condition,
load on bike, percent of grade on hills and
mt. passes on your route and others come into play.
The last two tours I was on a early 80's touring bike with upgraded parts.
I learned also to go with quality tires suitable for touring and bring a spare folding one just in case.
Good luck on your upcoming adventure.
I look back fondly on the ones I did.
They were quite challenging but very rewarding.