I'm a millennial and I think you summed it up pretty well.
The ironic thing is that boomers--the generation that threw off dress codes and produced the anti-war, civil rights, environmental, women's, and LBGT+ movements didn't have that mindset, but their parents and grandparents did.
Gen X very much became the boomers they hated. Half of the millennials I've known for years have become identical to the boomers they complained about 10 years ago. The millennials I know complain about zoomers being lazy and not pulling themselves up by their bootstraps and using strange lingo and being addicted to things their generation wouldn't have tolerated. And they things they like suck but the thing millennials liked were "good".
Basically, boomer is anyone older than you and acts like a grumpy or entitled old person. Zoomer is anyone younger than you who makes you uncomfortable with your age.