Boomers don't "start at 40" unless you meant birthdates in the 1940's

"boomer" actually refers to the generation known as baby boomers who were born post -WW2 and post-great-depression between 1946 and 1964. They'd be in the late 50's to 70's age wise.

GenX is 1975-1980, so that's early 40 to 50yo for them. They were followed by millennials from 1981-1994.

Every generation has its assholes. Boomers may be more visible because there's a lot of them. The term "baby boomers" literally refers to a period with higher birth rates and decreasing infant mortality.

The other part of the equation is that the world kinda went crazy in terms of rate of change. The early 19xx's saw things like air conditioning, television, women's voting rights (USA) and home refrigerators. A lot of this was in the 20's but didn't necessarily become commonplace until after and was followed by planes, jets, rockets that could reach space, the internet etc. The birth-control pill in the 50's was another underrated impact on society.

So boomers are a large generation of plenty, but also a generation of plenty-of-change, absentee/post-war parents, massive technological impact on the workplace etc etc. If some are a bit of Luddites it might be worth considering that they often grew up on the cusp of a technological revolution but then were expected to use it in the workplace as it replaced many previous resources. As a generation, they are still highly visible in society today, and of course shit floats to the top.

In terms of assholes, I've met plenty in genX (my generation) and millennials, though the latter are often split among whether they were lucky enough to get into a house or not before stuff went apeshit in that market.