These are airliners not tactical jets. An airport isn’t dramatically different from an office building in terms of physical demand. Being at a client site 100 days could be 50 flights if you’re on a typical Mon-Thurs consulting schedule and home every weekend.

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.