So the parameters for the zillenial generation seem to be all over the place depending on who you ask. Some people put it as far back as 1993 or even 1991.
I was in my late teens/early 20s when the culture started to shift, so I got exposed to zillenial pop culture and was still within the marketing demographic. I can still kinda vibe with zillenials because we do have some experiences in common. It's not like there's much difference between your late 20s and your early 30s anyway.
That being said, I feel like my childhood was absolutely more millenial than gen z. I grew up poor so we didn't have cable until I was 8, and I have very clear memories of dial up internet which we kept until 2004 or so. I still got to enjoy classic late 90s cartoons like Hey Arnold, Spongebob, The Wild Thornberries, and Rocket Power, just a teeny bit later than when they originally aired. And I did have the same pop culture experience as my elder millenial cousins, it was just the more tween-friendly version that I got from my Girls Life and Discovery Girl magazines.
I also still remember 9/11 pretty clearly. Being in second grade, I was too young to fully understand the political implications. However, I do remember being actively scared, and the impact of the event was strong enough to affect my worldview.
As for zillenial/zoomer childhood experiences, I played with Bratz dolls and visited Everythinggirl.com, but was too old for Webkinz when they came out. I watched Ned's Declassified and Zoey 101, but had long outgrown Nickelodeon once Victorious came on. Even when iCarly came out, my taste in media was already taking an edgier and more mature direction.
Personally, I'd put the zillenial marker at around 1995/96, but I wanna hear what y'all think!