No, I do not think what we've witnessed altered our mental state. Your instructor is challenging you to research whether the effect of a lifetime of witnessing traumatic events is cumulative. What acuity is lost is sometimes natural with time, even spent in utopia. Those who keep food over-supplied in memory of the great depression understand the nature of free enterprise, that it rises and falls, and though that food may be an unnecessary habit, it certainly isn't now, in this recurrent downfall.
"Decay" is an inaccurate concept of yours. And remember with all these decades of living, between every traumatic event were long periods of industrious productivity, enjoyment of the outdoors, joy of babies and children, cherishing of pets, the general replenishing sources of strength and reflection we all spend a great deal more time than traumatic events take. War veterans recover or not as individually as dementia strikes individually or not.
Though it is common for youth to dread aging, in most cases it is a sad misconception. The immediacy and fragility of living is appreciated more sharply witnessing traumatic events, being reminded any of those catastrophes could have involved you instead, but for geography. In cases such as both Kennedy assassinations, King's, and all other events that change American direction, it does indeed happen to you, necessitating adaption. In cases such as earthquakes, mine collapses, hurricanes, fires, and volcano eruptions, you learn the depth of empathy. In cases such as murder, rape, child molestation, and other crimes, your awareness of the ugly side of living balances with perspective, and appreciation that it wasn't you. In so many cases, overall, life is arbitrary and depends on variables.
A Good Age by Alex Comfort, a perfect source for your assignment.