I work with a 75 year olds who is on the road 100+ days each year. He's happy, company is happy, and the job isn't very physically demanding. This will become more common
Even if driving, most 75 year olds are competent to drive and especially those still capable to work a travel job.
Flying that often, you learn how to make it easier. For out Sunday back Thursday night trips, I can travel in a backpack if I have to but usually used a 15-pound roller bag. Hardly the stuff of special forces and less strenuous than a round of golf, which plenty of 75 year olds do.
My in-laws are ~75. If you looked at them or watched them play one of their 100+ rounds of golf (walking) a year, you’d probably guess they were early 60s.
It’s apparent that I need to point out that this is a sub aimed towards ambitious people chasing their dream business/job/hobby/dream/interest/etc.
There might be a bias here towards thinking a strenuous job is normal, just because we might take in that level of stress voluntarily