The other name for the boomer generation is the "me" generation. because after the depression their parents had money again and gave them everything they wanted creating a generation of incredibly selfish people.
https://en.wikipedia.org/wiki/Me_generation
Just like an idiot, the typical boomer doesn't understand why the saying exists or why it was started. They focus on just the surface level, and assume the rule for usage is the same as the title.
Baby Boomer: The generation is often defined as people born from 1946 to 1964 during the mid-20th century baby boom. 1962 the birth control pills came. The Food and Drug Administration approved the first oral contraceptive in 1960. Within 2 years of its initial distribution, 1.2 million American women were using the birth control pill, or the "pill," as it is popularly known. This was the end of the baby boom.
Perhaps part of the reason they seem... different... to younger generations is related to the fact that there would have been a higher percentage of unwanted pregnancies for their cohort than the ones that followed.
The Pill became available right as the first wave of Boomers came of age. They were the first generation to have it available when they were at that college/marriage age. The Pill didn't end Boomers. The Pill is why there are so many fewer Gen Xers; because Boomers used The Pill. There was slower uptake among the parents.
Similar baby booms happened in other parts of the world, though the exact dates differ.
So somebody on the internet referring to boomers might mean people born in the late 60s as well.
Probably because it's a funny phrase, especially if you compare it to the English one. The English just sounds technical, while the German one seems to have a bit of a wink.