You say you’re 54, so by the study’s definition, you are Gen X, and are thus about twice as likely to have never been present for a mass shooting as a Millenial, about three times as likely to have never been present at a mass shooting as Gen Z.
See Table 3.

Exactly. I’m in my mid 30’s and know several people who have witnessed mass shootings. I have personally been under active shooter lockdowns multiple times. Hell, my former roommate was shot in the ass by one at a music festival. This person saw “7% have witnessed an active shooting” and immediately called bullshit, because they’re part of the other 93% and are incapable of imagining anything outside of their (extremely narrow) lived experience. And that’s some real boomer attitude.