And in actual usage...
I think to young people "Boomer" has become slang for anyone older than them. The old Hippie phrase "Never trust anyone older than 30" seems like more or less how they use it. By contrast, old people seem to use "Millennial" to refer to pretty much anyone younger than them. Meanwhile, Gen X just hides and hopes no one notices them, but if someone does, they expect to be called either a Boomer or a Millennial depending on who is addressing them.
True, the word has taken on a life of it's on.. with people using in new contexts all the time. But the anyone older then me sentiment is very popular.
This is the way I am use to seeing the word used, so much so, I thought this was the main meaning. Smile and Laugh.