Arthur,
I would submit to you the counterpoint of:
Perhaps there are other, more important factors that determine what makes someone a "healthy older person" vs. one of the "least health older people" (as you say).
It is pretty widely acknowledged that the Mediterranean diet and also much of the typical Asian diet is more healthy than what mass-market (especially with the broad-based generalization of lower income) Americans may eat. Diet/exercise attribute greatly to how healthy one may be, regardless of what nationality.
There are parts of Europe (I'm guessing UK) where BMI may be much closer to the typical US BMI, but that is just a guess on my part. With increased wealth in China, I've read that the younger population has an increased BMI.
But, I think you need more data points before you can draw a conclusion that using a rollaboard vs. a backpack is indicative that someone has "given up" and (as you say) "that's when you've taken the final plunge into true decrepitude and Old Codger-hood."
Could it be that persons who have chosen to use scooters or other assistance devices that you might see out and about are just that "out and about," trying to live as independently as possible. I see many older Americans (some with assistance devices) when I travel, who may take a little longer to arrive at their destinations or who may take a little longer entering or exiting transportation, and when they apologize, I simply smile and tell them how inspiring they are to me: They are still living every ounce of life and still going. If someone can make that choice, power to them.....sure beats sitting at home miserable being that sour person that no one calls, no one comes to visit because they may have lost their zest/joy for life.
Let's be careful not to judge.
Genetics also factor into one's health. But, yes, there are choices every single person can make every single day that can also impact his/her health.....food choices, exercise choices, lifestyle choices, attitude choices...........BUT don't be too hard on those who may have made mostly good choices, but the genetics are just against them. I wish you many years of the ability to haul your backpack and keep going. There are many people who would love to trade places with you, and many of those people may have been doing exactly what you are doing as recently as five years ago. Situations change, and I sincerely hope you never have to experience a negative physical situation. But, please use caution judging others or drawing conclusions solely based on what kind of luggage they use.
I also hope that IF the time comes that you need an assistance device to still go out and about, that you won't be so proud as to not use it....that you won't become a sour old guy who is too proud to stay out and about enjoying life to the fullest that is possible WITH the assistance available.......THAT would be unhealthy, and THAT would be giving up.
There are people in life that "collect people," and those that wonder where everyone went. My 87-year old neighbors are good examples of people who "collect people ." After living full, active lives and many travels, they just can't do it any more. They get out and about slowly and with assistance devices. When they physically can't get out, they are overwhelmed with food and good deeds that come their way. I tell them they have planted their garden, tended their garden, and now they can enjoy the harvest of the relationships they have developed with others. They have not (as you say) "taken the final plunge into true decrepitude and Old Codger-hood." They are still living, contributing and enjoying life, and we all love having them around. Every time we travel, they can't wait to hear about our travels, smiling as they recall their many travels. They are living contributing and joyful lives.
More data points are needed.....caution in making broad-based conclusions without full information.