Forget older adults, this is for everyone. If you have a step width that affords knee over foot, hip over knee, and you load those stacked joints, there will be less peak adduction and abduction loads at the knees . . . . and less risk for frontal plane drift of the hip-pelvis, improved control of limb rotation during loading, and reduced risks for over pronation at the foot-ankle complex. These are anti-cross over gait principles.
And, this is obviously not just a stair descent or ascent issue, these are normal fundamental gait (walk and run) principles that just make good common sense !
Knee. 2014 Aug;21(4):821-6. doi: 10.1016/j.knee.2014.03.006. Epub 2014 Apr 3.