[bcrl]

It is more a question of frequency. That is, the elderly deteriorate quickly more frequently than younger folks do. Younger folks can still deteriorate quickly under the right circumstances, but at a population level, that is a much lower frequency given that the average younger adult has more resilient immune system and greater muscle mass than someone in their later years.

Heck, I'm in reasonably good health, but if I get hit by a car crossing the road this evening, I could deteriorate quickly overnight due to injuries and be dead tomorrow. It's just less likely for me than it is for an elderly person that has poor vision and moves slowly while crossing the road as I am more likely to be able to spot a hazard and move out of the way.