The word "Boomer" is short for "Baby Boomer" which refers to people who were born after World War II and up until the early sixties. There were more births during that time than usual, which was referred to as a "baby boom", thus the name.
FYI there are more Millennials than there are "Baby Boomers".
>"boomers effectively lived their whole life in the same world we are in"
If you mean that literally, yes, everyone who has ever lived has lived in this world.
But there has been more change in the world in this short time since World War II than perhaps in any time in history, except perhaps during the late Renaissance in the 17th century.
The world today doesn't resemble the world of the late forties at all. Not even close.