Having been there a couple times, and even up higher in Potosi, when I was scouting around for a potential area to ex-pat it some day, I learned that for elderly people, it's more of a hardship/risk when you live past the 6000 foot threshold. And with La Paz, we're looking at 12,500/ 13,500 in El Alto where the Airport is.
Given the hardship the poor can face down there, I did witness, what appeared to be, elderly women, with big sacks of potatoes, scaling those near-vertical cliffs in La Paz.
And I had a devil of a time climbing up 3 hilly streets to my hotel, empty-handed!
Once on a flat area, no problems, like walking around El Alto.